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 $82.39   10.683%   $91.1917   $91.19   $91.20   $91.20  
  Purchase #2 $52.42   12.249%   $58.8409   $58.84   $58.85   $58.80  
  Purchase #3 $213.96   8.842%   $232.8783   $232.88   $232.90   $232.90  
  Purchase #4 $186.85   12.519%   $210.2418   $210.24   $210.25   $210.20  
  Purchase #5 $75.49   12.512%   $84.9353   $84.94   $84.95   $84.90  
  Purchase #6 $236.43   8.760%   $257.1413   $257.14   $257.15   $257.10  
  Purchase #7 $108.40   4.260%   $113.0178   $113.02   $113.00   $113.00  
  7 purchase totals = $955.94       $1,048.2471   $1,048.25   $1,048.30   $1,048.10