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 $226.61   8.561%   $246.0101   $246.01   $246.00   $246.00  
  Purchase #2 $152.71   9.672%   $167.4801   $167.48   $167.50   $167.50  
  Purchase #3 $220.75   7.268%   $236.7941   $236.79   $236.80   $236.80  
  Purchase #4 $128.43   13.817%   $146.1752   $146.18   $146.20   $146.20  
  Purchase #5 $61.90   11.785%   $69.1949   $69.19   $69.20   $69.20  
  Purchase #6 $28.55   3.560%   $29.5664   $29.57   $29.55   $29.60  
  Purchase #7 $212.46   5.746%   $224.668   $224.67   $224.65   $224.70  
  7 purchase totals = $1,031.41       $1,119.8888   $1,119.89   $1,119.90   $1,120.00