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 $64.73   6.603%   $69.0041   $69.00   $69.00   $69.00  
  Purchase #2 $96.92   10.376%   $106.9764   $106.98   $107.00   $107.00  
  Purchase #3 $151.53   9.629%   $166.1208   $166.12   $166.10   $166.10  
  Purchase #4 $247.88   9.704%   $271.9343   $271.93   $271.95   $271.90  
  Purchase #5 $148.87   6.324%   $158.2845   $158.28   $158.30   $158.30  
  Purchase #6 $208.51   11.613%   $232.7243   $232.72   $232.70   $232.70  
  Purchase #7 $105.83   4.539%   $110.6336   $110.63   $110.65   $110.60  
  7 purchase totals = $1,024.27       $1,115.6780   $1,115.66   $1,115.70   $1,115.60