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 $125.88   9.471%   $137.8021   $137.80   $137.80   $137.80  
  Purchase #2 $23.86   7.392%   $25.6237   $25.62   $25.60   $25.60  
  Purchase #3 $163.32   8.386%   $177.016   $177.02   $177.00   $177.00  
  Purchase #4 $87.55   12.776%   $98.7354   $98.74   $98.75   $98.70  
  Purchase #5 $103.58   11.408%   $115.3964   $115.40   $115.40   $115.40  
  Purchase #6 $199.79   12.422%   $224.6079   $224.61   $224.60   $224.60  
  Purchase #7 $205.44   13.482%   $233.1374   $233.14   $233.15   $233.10  
  7 purchase totals = $909.42       $1,012.3189   $1,012.33   $1,012.30   $1,012.20