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 $86.51   11.474%   $96.4362   $96.44   $96.45   $96.40  
  Purchase #2 $173.93   4.501%   $181.7586   $181.76   $181.75   $181.80  
  Purchase #3 $190.90   11.166%   $212.2159   $212.22   $212.20   $212.20  
  Purchase #4 $15.31   3.584%   $15.8587   $15.86   $15.85   $15.90  
  Purchase #5 $93.44   10.482%   $103.2344   $103.23   $103.25   $103.20  
  Purchase #6 $166.90   8.118%   $180.4489   $180.45   $180.45   $180.40  
  Purchase #7 $232.86   11.709%   $260.1256   $260.13   $260.15   $260.10  
  7 purchase totals = $959.85       $1,050.0783   $1,050.09   $1,050.10   $1,050.00