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 $31.38   10.213%   $34.5848   $34.58   $34.60   $34.60  
  Purchase #2 $140.55   11.214%   $156.3113   $156.31   $156.30   $156.30  
  Purchase #3 $37.27   8.426%   $40.4104   $40.41   $40.40   $40.40  
  Purchase #4 $241.86   3.122%   $249.4109   $249.41   $249.40   $249.40  
  Purchase #5 $158.26   12.282%   $177.6975   $177.70   $177.70   $177.70  
  Purchase #6 $200.72   4.341%   $209.4333   $209.43   $209.45   $209.40  
  Purchase #7 $54.25   10.343%   $59.8611   $59.86   $59.85   $59.90  
  7 purchase totals = $864.29       $927.7093   $927.70   $927.70   $927.70