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 $169.64   10.118%   $186.8042   $186.80   $186.80   $186.80  
  Purchase #2 $249.87   11.247%   $277.9729   $277.97   $277.95   $278.00  
  Purchase #3 $213.97   6.844%   $228.6141   $228.61   $228.60   $228.60  
  Purchase #4 $247.59   13.847%   $281.8738   $281.87   $281.85   $281.90  
  Purchase #5 $35.60   9.853%   $39.1077   $39.11   $39.10   $39.10  
  Purchase #6 $101.87   4.501%   $106.4552   $106.46   $106.45   $106.50  
  Purchase #7 $116.60   8.749%   $126.8013   $126.80   $126.80   $126.80  
  7 purchase totals = $1,135.14       $1,247.6292   $1,247.62   $1,247.55   $1,247.70