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 $221.43   11.197%   $246.2235   $246.22   $246.20   $246.20  
  Purchase #2 $21.48   6.316%   $22.8367   $22.84   $22.85   $22.80  
  Purchase #3 $161.70   8.618%   $175.6353   $175.64   $175.65   $175.60  
  Purchase #4 $133.45   7.354%   $143.2639   $143.26   $143.25   $143.30  
  Purchase #5 $198.73   9.194%   $217.0012   $217.00   $217.00   $217.00  
  Purchase #6 $53.79   11.689%   $60.0775   $60.08   $60.10   $60.10  
  Purchase #7 $147.29   9.665%   $161.5256   $161.53   $161.55   $161.50  
  7 purchase totals = $937.87       $1,026.5637   $1,026.57   $1,026.60   $1,026.50