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 $48.56   3.461%   $50.2407   $50.24   $50.25   $50.20  
  Purchase #2 $216.78   9.172%   $236.6631   $236.66   $236.65   $236.70  
  Purchase #3 $81.55   12.266%   $91.5529   $91.55   $91.55   $91.60  
  Purchase #4 $7.79   13.750%   $8.8611   $8.86   $8.85   $8.90  
  Purchase #5 $118.96   10.304%   $131.2176   $131.22   $131.20   $131.20  
  Purchase #6 $154.93   6.662%   $165.2514   $165.25   $165.25   $165.30  
  Purchase #7 $141.50   6.837%   $151.1744   $151.17   $151.15   $151.20  
  7 purchase totals = $770.07       $834.9612   $834.95   $834.90   $835.10