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 $41.51   5.428%   $43.7632   $43.76   $43.75   $43.80  
  Purchase #2 $65.87   4.659%   $68.9389   $68.94   $68.95   $68.90  
  Purchase #3 $168.57   7.648%   $181.4622   $181.46   $181.45   $181.50  
  Purchase #4 $167.39   4.162%   $174.3568   $174.36   $174.35   $174.40  
  Purchase #5 $235.94   12.607%   $265.685   $265.69   $265.70   $265.70  
  Purchase #6 $173.81   11.190%   $193.2593   $193.26   $193.25   $193.30  
  Purchase #7 $8.90   12.781%   $10.0375   $10.04   $10.05   $10.00  
  7 purchase totals = $861.99       $937.5029   $937.51   $937.50   $937.60