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 $57.96   8.676%   $62.9886   $62.99   $63.00   $63.00  
  Purchase #2 $214.51   13.750%   $244.0051   $244.01   $244.00   $244.00  
  Purchase #3 $151.45   6.860%   $161.8395   $161.84   $161.85   $161.80  
  Purchase #4 $130.73   11.746%   $146.0855   $146.09   $146.10   $146.10  
  Purchase #5 $190.99   6.515%   $203.433   $203.43   $203.45   $203.40  
  Purchase #6 $31.67   5.263%   $33.3368   $33.34   $33.35   $33.30  
  Purchase #7 $103.34   11.767%   $115.5   $115.50   $115.50   $115.50  
  7 purchase totals = $880.65       $967.1885   $967.20   $967.25   $967.10