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 $212.48   6.486%   $226.2615   $226.26   $226.25   $226.30  
  Purchase #2 $248.89   4.691%   $260.5654   $260.57   $260.55   $260.60  
  Purchase #3 $247.30   11.864%   $276.6397   $276.64   $276.65   $276.60  
  Purchase #4 $112.43   9.232%   $122.8095   $122.81   $122.80   $122.80  
  Purchase #5 $92.55   5.785%   $97.904   $97.90   $97.90   $97.90  
  Purchase #6 $164.29   10.594%   $181.6949   $181.69   $181.70   $181.70  
  Purchase #7 $89.85   10.575%   $99.3516   $99.35   $99.35   $99.40  
  7 purchase totals = $1,167.79       $1,265.2266   $1,265.22   $1,265.20   $1,265.30