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 $201.99   10.849%   $223.9039   $223.90   $223.90   $223.90  
  Purchase #2 $197.35   9.779%   $216.6489   $216.65   $216.65   $216.60  
  Purchase #3 $80.66   13.216%   $91.32   $91.32   $91.30   $91.30  
  Purchase #4 $71.75   5.578%   $75.7522   $75.75   $75.75   $75.80  
  Purchase #5 $116.48   5.681%   $123.0972   $123.10   $123.10   $123.10  
  Purchase #6 $159.83   6.417%   $170.0863   $170.09   $170.10   $170.10  
  Purchase #7 $119.99   4.295%   $125.1436   $125.14   $125.15   $125.10  
  7 purchase totals = $948.05       $1,025.9521   $1,025.95   $1,025.95   $1,025.90