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 $46.26   11.575%   $51.6146   $51.61   $51.60   $51.60  
  Purchase #2 $98.67   6.347%   $104.9326   $104.93   $104.95   $104.90  
  Purchase #3 $113.70   7.144%   $121.8227   $121.82   $121.80   $121.80  
  Purchase #4 $239.73   10.418%   $264.7051   $264.71   $264.70   $264.70  
  Purchase #5 $16.54   3.325%   $17.09   $17.09   $17.10   $17.10  
  Purchase #6 $248.29   12.700%   $279.8228   $279.82   $279.80   $279.80  
  Purchase #7 $222.77   11.783%   $249.019   $249.02   $249.00   $249.00  
  7 purchase totals = $985.96       $1,089.0068   $1,089.00   $1,088.95   $1,088.90