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 $54.46   10.814%   $60.3493   $60.35   $60.35   $60.30  
  Purchase #2 $167.80   9.596%   $183.9021   $183.90   $183.90   $183.90  
  Purchase #3 $144.36   9.357%   $157.8678   $157.87   $157.85   $157.90  
  Purchase #4 $13.84   5.470%   $14.597   $14.60   $14.60   $14.60  
  Purchase #5 $103.68   4.565%   $108.413   $108.41   $108.40   $108.40  
  Purchase #6 $163.37   4.688%   $171.0288   $171.03   $171.05   $171.00  
  Purchase #7 $108.63   11.165%   $120.7585   $120.76   $120.75   $120.80  
  7 purchase totals = $756.14       $816.9165   $816.92   $816.90   $816.90