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 $113.38   11.563%   $126.4901   $126.49   $126.50   $126.50  
  Purchase #2 $50.96   3.223%   $52.6024   $52.60   $52.60   $52.60  
  Purchase #3 $41.71   7.596%   $44.8783   $44.88   $44.90   $44.90  
  Purchase #4 $225.63   4.236%   $235.1877   $235.19   $235.20   $235.20  
  Purchase #5 $188.75   7.388%   $202.6949   $202.69   $202.70   $202.70  
  Purchase #6 $193.62   6.400%   $206.0117   $206.01   $206.00   $206.00  
  Purchase #7 $124.70   4.837%   $130.7317   $130.73   $130.75   $130.70  
  7 purchase totals = $938.75       $998.5968   $998.59   $998.65   $998.60