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 $246.63   12.258%   $276.8619   $276.86   $276.85   $276.90  
  Purchase #2 $83.30   5.386%   $87.7865   $87.79   $87.80   $87.80  
  Purchase #3 $181.28   11.461%   $202.0565   $202.06   $202.05   $202.10  
  Purchase #4 $164.26   7.469%   $176.5286   $176.53   $176.55   $176.50  
  Purchase #5 $173.25   9.636%   $189.9444   $189.94   $189.95   $189.90  
  Purchase #6 $96.73   4.540%   $101.1215   $101.12   $101.10   $101.10  
  Purchase #7 $210.49   11.640%   $234.991   $234.99   $235.00   $235.00  
  7 purchase totals = $1,155.94       $1,269.2904   $1,269.29   $1,269.30   $1,269.30