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 $68.41   10.178%   $75.3728   $75.37   $75.35   $75.40  
  Purchase #2 $117.42   13.426%   $133.1848   $133.18   $133.20   $133.20  
  Purchase #3 $215.67   6.858%   $230.4606   $230.46   $230.45   $230.50  
  Purchase #4 $234.49   5.625%   $247.6801   $247.68   $247.70   $247.70  
  Purchase #5 $6.35   7.280%   $6.8123   $6.81   $6.80   $6.80  
  Purchase #6 $141.42   11.747%   $158.0326   $158.03   $158.05   $158.00  
  Purchase #7 $184.48   6.733%   $196.901   $196.90   $196.90   $196.90  
  7 purchase totals = $968.24       $1,048.4442   $1,048.43   $1,048.45   $1,048.50