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 $102.93   9.789%   $113.0058   $113.01   $113.00   $113.00  
  Purchase #2 $154.29   4.782%   $161.6681   $161.67   $161.65   $161.70  
  Purchase #3 $71.27   12.136%   $79.9193   $79.92   $79.90   $79.90  
  Purchase #4 $60.61   12.662%   $68.2844   $68.28   $68.30   $68.30  
  Purchase #5 $11.78   4.338%   $12.291   $12.29   $12.30   $12.30  
  Purchase #6 $58.69   6.405%   $62.4491   $62.45   $62.45   $62.40  
  Purchase #7 $167.60   12.278%   $188.1779   $188.18   $188.20   $188.20  
  7 purchase totals = $627.17       $685.7956   $685.80   $685.80   $685.80