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 $41.69   11.692%   $46.5644   $46.56   $46.55   $46.60  
  Purchase #2 $150.69   12.598%   $169.6739   $169.67   $169.65   $169.70  
  Purchase #3 $9.75   11.233%   $10.8452   $10.85   $10.85   $10.80  
  Purchase #4 $236.52   13.272%   $267.9109   $267.91   $267.90   $267.90  
  Purchase #5 $211.83   12.425%   $238.1499   $238.15   $238.15   $238.10  
  Purchase #6 $46.98   3.289%   $48.5252   $48.53   $48.55   $48.50  
  Purchase #7 $67.82   9.118%   $74.0038   $74.00   $74.00   $74.00  
  7 purchase totals = $765.28       $855.6733   $855.67   $855.65   $855.60