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 $58.35   8.426%   $63.2666   $63.27   $63.25   $63.30  
  Purchase #2 $217.46   13.627%   $247.0933   $247.09   $247.10   $247.10  
  Purchase #3 $129.77   12.457%   $145.9354   $145.94   $145.95   $145.90  
  Purchase #4 $84.46   12.830%   $95.2962   $95.30   $95.30   $95.30  
  Purchase #5 $123.39   6.328%   $131.1981   $131.20   $131.20   $131.20  
  Purchase #6 $188.44   8.280%   $204.0428   $204.04   $204.05   $204.00  
  Purchase #7 $91.35   5.719%   $96.5743   $96.57   $96.55   $96.60  
  7 purchase totals = $893.22       $983.4067   $983.41   $983.40   $983.40