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 $174.67   13.490%   $198.233   $198.23   $198.25   $198.20  
  Purchase #2 $83.46   13.746%   $94.9324   $94.93   $94.95   $94.90  
  Purchase #3 $84.25   4.752%   $88.2536   $88.25   $88.25   $88.30  
  Purchase #4 $122.43   8.781%   $133.1806   $133.18   $133.20   $133.20  
  Purchase #5 $172.66   12.334%   $193.9559   $193.96   $193.95   $194.00  
  Purchase #6 $194.98   8.823%   $212.1831   $212.18   $212.20   $212.20  
  Purchase #7 $46.68   11.870%   $52.2209   $52.22   $52.20   $52.20  
  7 purchase totals = $879.13       $972.9595   $972.95   $973.00   $973.00