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 $53.94   5.678%   $57.0027   $57.00   $57.00   $57.00  
  Purchase #2 $87.58   4.221%   $91.2768   $91.28   $91.30   $91.30  
  Purchase #3 $91.91   8.438%   $99.6654   $99.67   $99.65   $99.70  
  Purchase #4 $167.31   6.607%   $178.3642   $178.36   $178.35   $178.40  
  Purchase #5 $100.41   6.648%   $107.0853   $107.09   $107.10   $107.10  
  Purchase #6 $205.60   4.694%   $215.2509   $215.25   $215.25   $215.30  
  Purchase #7 $21.36   12.400%   $24.0086   $24.01   $24.00   $24.00  
  7 purchase totals = $728.11       $772.6539   $772.66   $772.65   $772.80