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 $22.27   10.482%   $24.6043   $24.60   $24.60   $24.60  
  Purchase #2 $175.79   11.553%   $196.099   $196.10   $196.10   $196.10  
  Purchase #3 $74.82   9.331%   $81.8015   $81.80   $81.80   $81.80  
  Purchase #4 $200.53   8.492%   $217.559   $217.56   $217.55   $217.60  
  Purchase #5 $83.47   12.308%   $93.7435   $93.74   $93.75   $93.70  
  Purchase #6 $100.33   8.242%   $108.5992   $108.60   $108.60   $108.60  
  Purchase #7 $42.84   4.549%   $44.7888   $44.79   $44.80   $44.80  
  7 purchase totals = $700.05       $767.1953   $767.19   $767.20   $767.20