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 $49.61   6.739%   $52.9532   $52.95   $52.95   $53.00  
  Purchase #2 $67.43   9.264%   $73.6767   $73.68   $73.70   $73.70  
  Purchase #3 $168.30   12.398%   $189.1658   $189.17   $189.15   $189.20  
  Purchase #4 $45.98   7.248%   $49.3126   $49.31   $49.30   $49.30  
  Purchase #5 $250.69   5.122%   $263.5303   $263.53   $263.55   $263.50  
  Purchase #6 $17.61   3.148%   $18.1644   $18.16   $18.15   $18.20  
  Purchase #7 $213.30   11.650%   $238.1495   $238.15   $238.15   $238.10  
  7 purchase totals = $812.92       $884.9525   $884.95   $884.95   $885.00