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 $67.82   11.494%   $75.6152   $75.62   $75.60   $75.60  
  Purchase #2 $225.96   6.283%   $240.1571   $240.16   $240.15   $240.20  
  Purchase #3 $219.73   13.786%   $250.022   $250.02   $250.00   $250.00  
  Purchase #4 $237.45   13.256%   $268.9264   $268.93   $268.95   $268.90  
  Purchase #5 $227.69   3.372%   $235.3677   $235.37   $235.35   $235.40  
  Purchase #6 $108.63   4.600%   $113.627   $113.63   $113.65   $113.60  
  Purchase #7 $112.57   10.810%   $124.7388   $124.74   $124.75   $124.70  
  7 purchase totals = $1,199.85       $1,308.4542   $1,308.47   $1,308.45   $1,308.40