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 $65.89   3.361%   $68.1046   $68.10   $68.10   $68.10  
  Purchase #2 $230.75   7.562%   $248.1993   $248.20   $248.20   $248.20  
  Purchase #3 $53.90   10.589%   $59.6075   $59.61   $59.60   $59.60  
  Purchase #4 $239.39   10.223%   $263.8628   $263.86   $263.85   $263.90  
  Purchase #5 $196.86   4.640%   $205.9943   $205.99   $206.00   $206.00  
  Purchase #6 $151.34   12.682%   $170.5329   $170.53   $170.55   $170.50  
  Purchase #7 $15.83   12.670%   $17.8357   $17.84   $17.85   $17.80  
  7 purchase totals = $953.96       $1,034.1371   $1,034.13   $1,034.15   $1,034.10