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 $216.27   13.782%   $246.0763   $246.08   $246.10   $246.10  
  Purchase #2 $94.31   7.537%   $101.4181   $101.42   $101.40   $101.40  
  Purchase #3 $170.40   11.254%   $189.5768   $189.58   $189.60   $189.60  
  Purchase #4 $214.97   3.392%   $222.2618   $222.26   $222.25   $222.30  
  Purchase #5 $224.74   7.266%   $241.0696   $241.07   $241.05   $241.10  
  Purchase #6 $20.71   10.192%   $22.8208   $22.82   $22.80   $22.80  
  Purchase #7 $54.43   4.244%   $56.74   $56.74   $56.75   $56.70  
  7 purchase totals = $995.83       $1,079.9634   $1,079.97   $1,079.95   $1,080.00