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 $58.65   8.382%   $63.566   $63.57   $63.55   $63.60  
  Purchase #2 $27.37   6.171%   $29.059   $29.06   $29.05   $29.10  
  Purchase #3 $36.38   11.108%   $40.4211   $40.42   $40.40   $40.40  
  Purchase #4 $206.38   7.545%   $221.9514   $221.95   $221.95   $222.00  
  Purchase #5 $235.52   3.412%   $243.5559   $243.56   $243.55   $243.60  
  Purchase #6 $31.96   6.515%   $34.0422   $34.04   $34.05   $34.00  
  Purchase #7 $155.53   11.604%   $173.5777   $173.58   $173.60   $173.60  
  7 purchase totals = $751.79       $806.1733   $806.18   $806.15   $806.30