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 $102.55   8.227%   $110.9868   $110.99   $111.00   $111.00  
  Purchase #2 $230.93   8.655%   $250.917   $250.92   $250.90   $250.90  
  Purchase #3 $68.79   7.218%   $73.7553   $73.76   $73.75   $73.80  
  Purchase #4 $55.77   12.787%   $62.9013   $62.90   $62.90   $62.90  
  Purchase #5 $240.47   4.160%   $250.4736   $250.47   $250.45   $250.50  
  Purchase #6 $221.71   9.600%   $242.9942   $242.99   $243.00   $243.00  
  Purchase #7 $28.49   11.146%   $31.6655   $31.67   $31.65   $31.70  
  7 purchase totals = $948.71       $1,023.6937   $1,023.70   $1,023.65   $1,023.80