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 $168.94   10.113%   $186.0249   $186.02   $186.00   $186.00  
  Purchase #2 $158.63   8.593%   $172.2611   $172.26   $172.25   $172.30  
  Purchase #3 $202.48   7.610%   $217.8887   $217.89   $217.90   $217.90  
  Purchase #4 $79.80   13.375%   $90.4733   $90.47   $90.45   $90.50  
  Purchase #5 $188.37   3.787%   $195.5036   $195.50   $195.50   $195.50  
  Purchase #6 $100.92   8.319%   $109.3155   $109.32   $109.30   $109.30  
  Purchase #7 $189.59   7.362%   $203.5476   $203.55   $203.55   $203.50  
  7 purchase totals = $1,088.73       $1,175.0147   $1,175.01   $1,174.95   $1,175.00