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 $141.39   12.292%   $158.7697   $158.77   $158.75   $158.80  
  Purchase #2 $206.92   13.477%   $234.8066   $234.81   $234.80   $234.80  
  Purchase #3 $174.68   6.652%   $186.2997   $186.30   $186.30   $186.30  
  Purchase #4 $195.53   12.187%   $219.3592   $219.36   $219.35   $219.40  
  Purchase #5 $128.39   5.613%   $135.5965   $135.60   $135.60   $135.60  
  Purchase #6 $54.47   10.518%   $60.1992   $60.20   $60.20   $60.20  
  Purchase #7 $205.44   3.256%   $212.1291   $212.13   $212.15   $212.10  
  7 purchase totals = $1,106.82       $1,207.1600   $1,207.17   $1,207.15   $1,207.20