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 $225.95   5.282%   $237.8847   $237.88   $237.90   $237.90  
  Purchase #2 $46.47   6.809%   $49.6341   $49.63   $49.65   $49.60  
  Purchase #3 $98.32   6.608%   $104.817   $104.82   $104.80   $104.80  
  Purchase #4 $212.95   10.699%   $235.7335   $235.73   $235.75   $235.70  
  Purchase #5 $95.34   3.787%   $98.9505   $98.95   $98.95   $99.00  
  Purchase #6 $103.65   4.333%   $108.1412   $108.14   $108.15   $108.10  
  Purchase #7 $178.45   11.660%   $199.2573   $199.26   $199.25   $199.30  
  7 purchase totals = $961.13       $1,034.4183   $1,034.41   $1,034.45   $1,034.40