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 $94.63   9.596%   $103.7107   $103.71   $103.70   $103.70  
  Purchase #2 $212.31   6.308%   $225.7025   $225.70   $225.70   $225.70  
  Purchase #3 $166.54   8.253%   $180.2845   $180.28   $180.30   $180.30  
  Purchase #4 $221.78   6.145%   $235.4084   $235.41   $235.40   $235.40  
  Purchase #5 $31.75   10.573%   $35.1069   $35.11   $35.10   $35.10  
  Purchase #6 $144.41   4.859%   $151.4269   $151.43   $151.45   $151.40  
  Purchase #7 $173.59   9.803%   $190.607   $190.61   $190.60   $190.60  
  7 purchase totals = $1,045.01       $1,122.2469   $1,122.25   $1,122.25   $1,122.20