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 $91.52   8.739%   $99.5179   $99.52   $99.50   $99.50  
  Purchase #2 $194.42   11.325%   $216.4381   $216.44   $216.45   $216.40  
  Purchase #3 $38.67   13.867%   $44.0324   $44.03   $44.05   $44.00  
  Purchase #4 $221.34   9.255%   $241.825   $241.83   $241.85   $241.80  
  Purchase #5 $129.51   5.606%   $136.7703   $136.77   $136.75   $136.80  
  Purchase #6 $166.90   3.664%   $173.0152   $173.02   $173.00   $173.00  
  Purchase #7 $126.87   10.425%   $140.0962   $140.10   $140.10   $140.10  
  7 purchase totals = $969.23       $1,051.6951   $1,051.71   $1,051.70   $1,051.60