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 $50.31   4.408%   $52.5277   $52.53   $52.55   $52.50  
  Purchase #2 $216.43   5.347%   $228.0025   $228.00   $228.00   $228.00  
  Purchase #3 $73.86   13.353%   $83.7225   $83.72   $83.70   $83.70  
  Purchase #4 $53.34   3.479%   $55.1957   $55.20   $55.20   $55.20  
  Purchase #5 $223.55   3.835%   $232.1231   $232.12   $232.10   $232.10  
  Purchase #6 $93.50   10.768%   $103.5681   $103.57   $103.55   $103.60  
  Purchase #7 $227.95   13.542%   $258.819   $258.82   $258.80   $258.80  
  7 purchase totals = $938.94       $1,013.9586   $1,013.96   $1,013.90   $1,013.90