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 $180.96   8.284%   $195.9507   $195.95   $195.95   $196.00  
  Purchase #2 $44.88   4.492%   $46.896   $46.90   $46.90   $46.90  
  Purchase #3 $29.89   8.238%   $32.3523   $32.35   $32.35   $32.40  
  Purchase #4 $181.65   12.597%   $204.5325   $204.53   $204.55   $204.50  
  Purchase #5 $92.78   7.129%   $99.3943   $99.39   $99.40   $99.40  
  Purchase #6 $190.28   8.552%   $206.5527   $206.55   $206.55   $206.60  
  Purchase #7 $158.49   8.598%   $172.117   $172.12   $172.10   $172.10  
  7 purchase totals = $878.93       $957.7955   $957.79   $957.80   $957.90