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 $227.54   8.808%   $247.5817   $247.58   $247.60   $247.60  
  Purchase #2 $71.28   6.184%   $75.688   $75.69   $75.70   $75.70  
  Purchase #3 $31.44   6.611%   $33.5185   $33.52   $33.50   $33.50  
  Purchase #4 $106.77   10.640%   $118.1303   $118.13   $118.15   $118.10  
  Purchase #5 $70.71   5.791%   $74.8048   $74.80   $74.80   $74.80  
  Purchase #6 $92.97   11.438%   $103.6039   $103.60   $103.60   $103.60  
  Purchase #7 $168.78   8.203%   $182.625   $182.63   $182.65   $182.60  
  7 purchase totals = $769.49       $835.9522   $835.95   $836.00   $835.90