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 $56.62   8.468%   $61.4146   $61.41   $61.40   $61.40  
  Purchase #2 $217.65   13.381%   $246.7737   $246.77   $246.75   $246.80  
  Purchase #3 $162.39   8.659%   $176.4514   $176.45   $176.45   $176.50  
  Purchase #4 $125.86   4.646%   $131.7075   $131.71   $131.70   $131.70  
  Purchase #5 $108.72   9.483%   $119.0299   $119.03   $119.05   $119.00  
  Purchase #6 $84.32   11.865%   $94.3246   $94.32   $94.30   $94.30  
  Purchase #7 $216.54   3.424%   $223.9543   $223.95   $223.95   $224.00  
  7 purchase totals = $972.10       $1,053.6560   $1,053.64   $1,053.60   $1,053.70