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 $45.56   6.852%   $48.6818   $48.68   $48.70   $48.70  
  Purchase #2 $162.54   13.814%   $184.9933   $184.99   $185.00   $185.00  
  Purchase #3 $164.71   8.697%   $179.0348   $179.03   $179.05   $179.00  
  Purchase #4 $170.66   12.549%   $192.0761   $192.08   $192.10   $192.10  
  Purchase #5 $168.38   5.160%   $177.0684   $177.07   $177.05   $177.10  
  Purchase #6 $234.92   5.176%   $247.0795   $247.08   $247.10   $247.10  
  Purchase #7 $213.31   12.782%   $240.5753   $240.58   $240.60   $240.60  
  7 purchase totals = $1,160.08       $1,269.5092   $1,269.51   $1,269.60   $1,269.60