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 $236.92   13.872%   $269.7855   $269.79   $269.80   $269.80  
  Purchase #2 $168.96   12.272%   $189.6948   $189.69   $189.70   $189.70  
  Purchase #3 $184.67   7.380%   $198.2986   $198.30   $198.30   $198.30  
  Purchase #4 $240.95   8.113%   $260.4983   $260.50   $260.50   $260.50  
  Purchase #5 $62.50   9.338%   $68.3363   $68.34   $68.35   $68.30  
  Purchase #6 $60.66   11.518%   $67.6468   $67.65   $67.65   $67.60  
  Purchase #7 $16.28   11.634%   $18.174   $18.17   $18.15   $18.20  
  7 purchase totals = $970.94       $1,072.4343   $1,072.44   $1,072.45   $1,072.40