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 $69.95   7.151%   $74.9521   $74.95   $74.95   $75.00  
  Purchase #2 $219.50   13.582%   $249.3125   $249.31   $249.30   $249.30  
  Purchase #3 $102.63   5.663%   $108.4419   $108.44   $108.45   $108.40  
  Purchase #4 $149.27   10.678%   $165.2091   $165.21   $165.20   $165.20  
  Purchase #5 $67.86   11.727%   $75.8179   $75.82   $75.80   $75.80  
  Purchase #6 $45.95   11.383%   $51.1805   $51.18   $51.20   $51.20  
  Purchase #7 $38.79   3.536%   $40.1616   $40.16   $40.15   $40.20  
  7 purchase totals = $693.95       $765.0756   $765.07   $765.05   $765.10