Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $247.98   8.156%   $268.2052   $268.21   $268.20   $268.20  
  Purchase #2 $187.87   12.667%   $211.6675   $211.67   $211.65   $211.70  
  Purchase #3 $238.29   12.294%   $267.5854   $267.59   $267.60   $267.60  
  Purchase #4 $101.48   3.799%   $105.3352   $105.34   $105.35   $105.30  
  Purchase #5 $203.74   5.757%   $215.4693   $215.47   $215.45   $215.50  
  Purchase #6 $97.91   12.145%   $109.8012   $109.80   $109.80   $109.80  
  Purchase #7 $210.30   10.710%   $232.8231   $232.82   $232.80   $232.80  
  7 purchase totals = $1,287.57       $1,410.8869   $1,410.90   $1,410.85   $1,410.90