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 $194.49   6.111%   $206.3753   $206.38   $206.40   $206.40  
  Purchase #2 $126.95   4.592%   $132.7795   $132.78   $132.80   $132.80  
  Purchase #3 $236.60   4.216%   $246.5751   $246.58   $246.60   $246.60  
  Purchase #4 $238.71   6.663%   $254.6152   $254.62   $254.60   $254.60  
  Purchase #5 $117.43   9.592%   $128.6939   $128.69   $128.70   $128.70  
  Purchase #6 $160.71   6.181%   $170.6435   $170.64   $170.65   $170.60  
  Purchase #7 $51.30   5.600%   $54.1728   $54.17   $54.15   $54.20  
  7 purchase totals = $1,126.19       $1,193.8553   $1,193.86   $1,193.90   $1,193.90