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 $204.51   11.828%   $228.6994   $228.70   $228.70   $228.70  
  Purchase #2 $103.93   3.328%   $107.3888   $107.39   $107.40   $107.40  
  Purchase #3 $189.42   7.616%   $203.8462   $203.85   $203.85   $203.80  
  Purchase #4 $80.64   12.732%   $90.9071   $90.91   $90.90   $90.90  
  Purchase #5 $18.94   9.571%   $20.7527   $20.75   $20.75   $20.80  
  Purchase #6 $206.70   5.288%   $217.6303   $217.63   $217.65   $217.60  
  Purchase #7 $144.27   7.583%   $155.21   $155.21   $155.20   $155.20  
  7 purchase totals = $948.41       $1,024.4345   $1,024.44   $1,024.45   $1,024.40