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 $178.28   6.116%   $189.1836   $189.18   $189.20   $189.20  
  Purchase #2 $207.41   11.794%   $231.8719   $231.87   $231.85   $231.90  
  Purchase #3 $232.97   7.314%   $250.0094   $250.01   $250.00   $250.00  
  Purchase #4 $248.55   5.504%   $262.2302   $262.23   $262.25   $262.20  
  Purchase #5 $23.51   12.623%   $26.4777   $26.48   $26.50   $26.50  
  Purchase #6 $69.86   6.479%   $74.3862   $74.39   $74.40   $74.40  
  Purchase #7 $38.38   5.781%   $40.5987   $40.60   $40.60   $40.60  
  7 purchase totals = $998.96       $1,074.7577   $1,074.76   $1,074.80   $1,074.80