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 $143.73   10.245%   $158.4551   $158.46   $158.45   $158.50  
  Purchase #2 $9.35   4.185%   $9.7413   $9.74   $9.75   $9.70  
  Purchase #3 $146.37   9.507%   $160.2854   $160.29   $160.30   $160.30  
  Purchase #4 $9.73   13.681%   $11.0612   $11.06   $11.05   $11.10  
  Purchase #5 $169.85   5.558%   $179.2903   $179.29   $179.30   $179.30  
  Purchase #6 $6.68   5.687%   $7.0599   $7.06   $7.05   $7.10  
  Purchase #7 $103.74   8.209%   $112.256   $112.26   $112.25   $112.30  
  7 purchase totals = $589.45       $638.1492   $638.16   $638.15   $638.30