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 $235.44   12.354%   $264.5263   $264.53   $264.55   $264.50  
  Purchase #2 $73.38   3.135%   $75.6805   $75.68   $75.70   $75.70  
  Purchase #3 $107.52   5.813%   $113.7701   $113.77   $113.75   $113.80  
  Purchase #4 $46.85   5.135%   $49.2557   $49.26   $49.25   $49.30  
  Purchase #5 $104.99   13.563%   $119.2298   $119.23   $119.25   $119.20  
  Purchase #6 $157.47   12.474%   $177.1128   $177.11   $177.10   $177.10  
  Purchase #7 $143.38   5.192%   $150.8243   $150.82   $150.80   $150.80  
  7 purchase totals = $869.03       $950.3995   $950.40   $950.40   $950.40