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 $197.44   3.698%   $204.7413   $204.74   $204.75   $204.70  
  Purchase #2 $181.54   11.106%   $201.7018   $201.70   $201.70   $201.70  
  Purchase #3 $151.39   11.349%   $168.5713   $168.57   $168.55   $168.60  
  Purchase #4 $148.97   6.293%   $158.3447   $158.34   $158.35   $158.30  
  Purchase #5 $188.75   11.720%   $210.8715   $210.87   $210.85   $210.90  
  Purchase #6 $88.30   9.185%   $96.4104   $96.41   $96.40   $96.40  
  Purchase #7 $244.84   8.209%   $264.9389   $264.94   $264.95   $264.90  
  7 purchase totals = $1,201.23       $1,305.5799   $1,305.57   $1,305.55   $1,305.50