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 $224.30   7.751%   $241.6855   $241.69   $241.70   $241.70  
  Purchase #2 $246.91   13.304%   $279.7589   $279.76   $279.75   $279.80  
  Purchase #3 $19.62   9.595%   $21.5025   $21.50   $21.50   $21.50  
  Purchase #4 $150.30   13.642%   $170.8039   $170.80   $170.80   $170.80  
  Purchase #5 $156.30   3.493%   $161.7596   $161.76   $161.75   $161.80  
  Purchase #6 $68.36   12.184%   $76.689   $76.69   $76.70   $76.70  
  Purchase #7 $78.90   8.694%   $85.7596   $85.76   $85.75   $85.80  
  7 purchase totals = $944.69       $1,037.9590   $1,037.96   $1,037.95   $1,038.10