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 $22.81   7.622%   $24.5486   $24.55   $24.55   $24.50  
  Purchase #2 $244.57   12.188%   $274.3782   $274.38   $274.40   $274.40  
  Purchase #3 $85.37   4.347%   $89.081   $89.08   $89.10   $89.10  
  Purchase #4 $201.65   8.199%   $218.1833   $218.18   $218.20   $218.20  
  Purchase #5 $126.61   5.712%   $133.842   $133.84   $133.85   $133.80  
  Purchase #6 $33.65   11.170%   $37.4087   $37.41   $37.40   $37.40  
  Purchase #7 $238.93   10.406%   $263.7931   $263.79   $263.80   $263.80  
  7 purchase totals = $953.59       $1,041.2349   $1,041.23   $1,041.30   $1,041.20