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 $95.63   6.140%   $101.5017   $101.50   $101.50   $101.50  
  Purchase #2 $219.81   9.385%   $240.4392   $240.44   $240.45   $240.40  
  Purchase #3 $179.94   5.862%   $190.4881   $190.49   $190.50   $190.50  
  Purchase #4 $239.47   9.869%   $263.1033   $263.10   $263.10   $263.10  
  Purchase #5 $24.65   8.611%   $26.7726   $26.77   $26.75   $26.80  
  Purchase #6 $185.40   9.127%   $202.3215   $202.32   $202.30   $202.30  
  Purchase #7 $34.96   3.508%   $36.1864   $36.19   $36.20   $36.20  
  7 purchase totals = $979.86       $1,060.8128   $1,060.81   $1,060.80   $1,060.80