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 $223.49   9.534%   $244.7975   $244.80   $244.80   $244.80  
  Purchase #2 $201.75   4.443%   $210.7138   $210.71   $210.70   $210.70  
  Purchase #3 $14.68   10.607%   $16.2371   $16.24   $16.25   $16.20  
  Purchase #4 $216.29   9.574%   $236.9976   $237.00   $237.00   $237.00  
  Purchase #5 $26.49   4.673%   $27.7279   $27.73   $27.75   $27.70  
  Purchase #6 $135.65   6.265%   $144.1485   $144.15   $144.15   $144.10  
  Purchase #7 $155.29   8.109%   $167.8825   $167.88   $167.90   $167.90  
  7 purchase totals = $973.64       $1,048.5049   $1,048.51   $1,048.55   $1,048.40