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 $165.58   8.515%   $179.6791   $179.68   $179.70   $179.70  
  Purchase #2 $171.96   9.370%   $188.0727   $188.07   $188.05   $188.10  
  Purchase #3 $59.87   10.733%   $66.2958   $66.30   $66.30   $66.30  
  Purchase #4 $196.66   10.660%   $217.624   $217.62   $217.60   $217.60  
  Purchase #5 $118.49   5.790%   $125.3506   $125.35   $125.35   $125.40  
  Purchase #6 $160.48   6.771%   $171.3461   $171.35   $171.35   $171.30  
  Purchase #7 $187.48   10.365%   $206.9123   $206.91   $206.90   $206.90  
  7 purchase totals = $1,060.52       $1,155.2806   $1,155.28   $1,155.25   $1,155.30