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 $205.53   7.537%   $221.0208   $221.02   $221.00   $221.00  
  Purchase #2 $52.97   5.640%   $55.9575   $55.96   $55.95   $56.00  
  Purchase #3 $57.27   11.281%   $63.7306   $63.73   $63.75   $63.70  
  Purchase #4 $165.93   10.373%   $183.1419   $183.14   $183.15   $183.10  
  Purchase #5 $142.29   8.348%   $154.1684   $154.17   $154.15   $154.20  
  Purchase #6 $156.83   6.473%   $166.9816   $166.98   $167.00   $167.00  
  Purchase #7 $97.52   11.116%   $108.3603   $108.36   $108.35   $108.40  
  7 purchase totals = $878.34       $953.3611   $953.36   $953.35   $953.40