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 $96.98   13.698%   $110.2643   $110.26   $110.25   $110.30  
  Purchase #2 $189.80   6.751%   $202.6134   $202.61   $202.60   $202.60  
  Purchase #3 $173.97   6.714%   $185.6503   $185.65   $185.65   $185.70  
  Purchase #4 $136.64   13.779%   $155.4676   $155.47   $155.45   $155.50  
  Purchase #5 $211.54   11.828%   $236.561   $236.56   $236.55   $236.60  
  Purchase #6 $8.62   12.262%   $9.677   $9.68   $9.70   $9.70  
  Purchase #7 $127.42   10.669%   $141.0144   $141.01   $141.00   $141.00  
  7 purchase totals = $944.97       $1,041.2480   $1,041.24   $1,041.20   $1,041.40