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 $126.97   3.487%   $131.3974   $131.40   $131.40   $131.40  
  Purchase #2 $85.61   12.464%   $96.2804   $96.28   $96.30   $96.30  
  Purchase #3 $229.89   3.224%   $237.3017   $237.30   $237.30   $237.30  
  Purchase #4 $95.79   12.204%   $107.4802   $107.48   $107.50   $107.50  
  Purchase #5 $5.41   6.301%   $5.7509   $5.75   $5.75   $5.80  
  Purchase #6 $54.92   9.620%   $60.2033   $60.20   $60.20   $60.20  
  Purchase #7 $138.58   3.577%   $143.537   $143.54   $143.55   $143.50  
  7 purchase totals = $737.17       $781.9509   $781.95   $782.00   $782.00