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 $68.29   12.443%   $76.7873   $76.79   $76.80   $76.80  
  Purchase #2 $97.81   5.777%   $103.4605   $103.46   $103.45   $103.50  
  Purchase #3 $10.83   8.515%   $11.7522   $11.75   $11.75   $11.80  
  Purchase #4 $156.61   5.456%   $165.1546   $165.15   $165.15   $165.20  
  Purchase #5 $112.97   7.870%   $121.8607   $121.86   $121.85   $121.90  
  Purchase #6 $240.79   5.231%   $253.3857   $253.39   $253.40   $253.40  
  Purchase #7 $201.65   8.279%   $218.3446   $218.34   $218.35   $218.30  
  7 purchase totals = $888.95       $950.7456   $950.74   $950.75   $950.90