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   9.232%   $74.5945   $74.59   $74.60   $74.60  
  Purchase #2 $11.49   3.146%   $11.8515   $11.85   $11.85   $11.90  
  Purchase #3 $57.95   3.717%   $60.104   $60.10   $60.10   $60.10  
  Purchase #4 $126.62   5.435%   $133.5018   $133.50   $133.50   $133.50  
  Purchase #5 $9.99   13.124%   $11.3011   $11.30   $11.30   $11.30  
  Purchase #6 $146.67   8.436%   $159.0431   $159.04   $159.05   $159.00  
  Purchase #7 $28.98   13.844%   $32.992   $32.99   $33.00   $33.00  
  7 purchase totals = $449.99       $483.3880   $483.37   $483.40   $483.40