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 $191.98   7.815%   $206.9832   $206.98   $207.00   $207.00  
  Purchase #2 $178.63   10.793%   $197.9095   $197.91   $197.90   $197.90  
  Purchase #3 $240.38   5.759%   $254.2235   $254.22   $254.20   $254.20  
  Purchase #4 $133.64   5.372%   $140.8191   $140.82   $140.80   $140.80  
  Purchase #5 $26.47   11.805%   $29.5948   $29.59   $29.60   $29.60  
  Purchase #6 $34.99   13.782%   $39.8123   $39.81   $39.80   $39.80  
  Purchase #7 $144.94   5.808%   $153.3581   $153.36   $153.35   $153.40  
  7 purchase totals = $951.03       $1,022.7005   $1,022.69   $1,022.65   $1,022.70