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 $59.98   5.129%   $63.0564   $63.06   $63.05   $63.10  
  Purchase #2 $128.56   9.599%   $140.9005   $140.90   $140.90   $140.90  
  Purchase #3 $164.80   6.708%   $175.8548   $175.85   $175.85   $175.90  
  Purchase #4 $117.99   9.430%   $129.1165   $129.12   $129.10   $129.10  
  Purchase #5 $13.92   3.165%   $14.3606   $14.36   $14.35   $14.40  
  Purchase #6 $155.70   6.345%   $165.5792   $165.58   $165.60   $165.60  
  Purchase #7 $34.35   6.540%   $36.5965   $36.60   $36.60   $36.60  
  7 purchase totals = $675.30       $725.4645   $725.47   $725.45   $725.60