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 $250.72   10.283%   $276.5015   $276.50   $276.50   $276.50  
  Purchase #2 $6.94   3.678%   $7.1953   $7.20   $7.20   $7.20  
  Purchase #3 $30.43   3.437%   $31.4759   $31.48   $31.50   $31.50  
  Purchase #4 $56.83   8.110%   $61.4389   $61.44   $61.45   $61.40  
  Purchase #5 $182.45   6.767%   $194.7964   $194.80   $194.80   $194.80  
  Purchase #6 $121.74   7.457%   $130.8182   $130.82   $130.80   $130.80  
  Purchase #7 $95.93   3.717%   $99.4957   $99.50   $99.50   $99.50  
  7 purchase totals = $745.04       $801.7219   $801.74   $801.75   $801.70