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 $60.53   8.579%   $65.7229   $65.72   $65.70   $65.70  
  Purchase #2 $222.49   5.831%   $235.4634   $235.46   $235.45   $235.50  
  Purchase #3 $180.70   9.409%   $197.7021   $197.70   $197.70   $197.70  
  Purchase #4 $27.60   8.628%   $29.9813   $29.98   $30.00   $30.00  
  Purchase #5 $144.31   5.511%   $152.2629   $152.26   $152.25   $152.30  
  Purchase #6 $45.51   11.254%   $50.6317   $50.63   $50.65   $50.60  
  Purchase #7 $136.30   11.175%   $151.5315   $151.53   $151.55   $151.50  
  7 purchase totals = $817.44       $883.2958   $883.28   $883.30   $883.30