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 $194.47   3.829%   $201.9163   $201.92   $201.90   $201.90  
  Purchase #2 $73.43   7.498%   $78.9358   $78.94   $78.95   $78.90  
  Purchase #3 $36.58   10.129%   $40.2852   $40.29   $40.30   $40.30  
  Purchase #4 $102.71   4.683%   $107.5199   $107.52   $107.50   $107.50  
  Purchase #5 $245.71   3.212%   $253.6022   $253.60   $253.60   $253.60  
  Purchase #6 $190.36   6.214%   $202.189   $202.19   $202.20   $202.20  
  Purchase #7 $39.43   10.300%   $43.4913   $43.49   $43.50   $43.50  
  7 purchase totals = $882.69       $927.9397   $927.95   $927.95   $927.90