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 $169.77   13.704%   $193.0353   $193.04   $193.05   $193.00  
  Purchase #2 $135.92   6.211%   $144.362   $144.36   $144.35   $144.40  
  Purchase #3 $39.27   13.423%   $44.5412   $44.54   $44.55   $44.50  
  Purchase #4 $99.79   4.125%   $103.9063   $103.91   $103.90   $103.90  
  Purchase #5 $50.52   12.741%   $56.9568   $56.96   $56.95   $57.00  
  Purchase #6 $27.71   10.177%   $30.53   $30.53   $30.55   $30.50  
  Purchase #7 $72.64   11.269%   $80.8258   $80.83   $80.85   $80.80  
  7 purchase totals = $595.62       $654.1574   $654.17   $654.20   $654.10