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 $64.96   6.137%   $68.9466   $68.95   $68.95   $68.90  
  Purchase #2 $181.44   13.232%   $205.4481   $205.45   $205.45   $205.40  
  Purchase #3 $217.32   13.845%   $247.408   $247.41   $247.40   $247.40  
  Purchase #4 $20.34   11.427%   $22.6643   $22.66   $22.65   $22.70  
  Purchase #5 $60.73   13.254%   $68.7792   $68.78   $68.80   $68.80  
  Purchase #6 $222.85   12.764%   $251.2946   $251.29   $251.30   $251.30  
  Purchase #7 $127.56   4.241%   $132.9698   $132.97   $132.95   $133.00  
  7 purchase totals = $895.20       $997.5106   $997.51   $997.50   $997.50