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 $212.60   11.316%   $236.6578   $236.66   $236.65   $236.70  
  Purchase #2 $13.76   3.458%   $14.2358   $14.24   $14.25   $14.20  
  Purchase #3 $80.47   6.317%   $85.5533   $85.55   $85.55   $85.60  
  Purchase #4 $163.84   9.343%   $179.1476   $179.15   $179.15   $179.10  
  Purchase #5 $75.52   11.347%   $84.0893   $84.09   $84.10   $84.10  
  Purchase #6 $196.50   9.673%   $215.5074   $215.51   $215.50   $215.50  
  Purchase #7 $140.53   4.199%   $146.4309   $146.43   $146.45   $146.40  
  7 purchase totals = $883.22       $961.6221   $961.63   $961.65   $961.60