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 $238.34   10.335%   $262.9724   $262.97   $262.95   $263.00  
  Purchase #2 $231.70   9.809%   $254.4275   $254.43   $254.45   $254.40  
  Purchase #3 $169.74   10.314%   $187.247   $187.25   $187.25   $187.20  
  Purchase #4 $199.30   13.137%   $225.482   $225.48   $225.50   $225.50  
  Purchase #5 $104.80   8.123%   $113.3129   $113.31   $113.30   $113.30  
  Purchase #6 $141.65   6.298%   $150.5711   $150.57   $150.55   $150.60  
  Purchase #7 $197.45   3.502%   $204.3647   $204.36   $204.35   $204.40  
  7 purchase totals = $1,282.98       $1,398.3776   $1,398.37   $1,398.35   $1,398.40