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 $201.46   5.289%   $212.1152   $212.12   $212.10   $212.10  
  Purchase #2 $167.86   4.824%   $175.9576   $175.96   $175.95   $176.00  
  Purchase #3 $37.69   9.778%   $41.3753   $41.38   $41.40   $41.40  
  Purchase #4 $235.50   3.173%   $242.9724   $242.97   $242.95   $243.00  
  Purchase #5 $56.77   13.333%   $64.3391   $64.34   $64.35   $64.30  
  Purchase #6 $115.56   3.347%   $119.4278   $119.43   $119.45   $119.40  
  Purchase #7 $182.42   9.347%   $199.4708   $199.47   $199.45   $199.50  
  7 purchase totals = $997.26       $1,055.6582   $1,055.67   $1,055.65   $1,055.70