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 $59.56   7.149%   $63.8179   $63.82   $63.80   $63.80  
  Purchase #2 $73.30   5.133%   $77.0625   $77.06   $77.05   $77.10  
  Purchase #3 $214.67   5.851%   $227.2303   $227.23   $227.25   $227.20  
  Purchase #4 $118.84   9.803%   $130.4899   $130.49   $130.50   $130.50  
  Purchase #5 $22.51   13.367%   $25.5189   $25.52   $25.50   $25.50  
  Purchase #6 $79.61   10.725%   $88.1482   $88.15   $88.15   $88.10  
  Purchase #7 $185.40   6.455%   $197.3676   $197.37   $197.35   $197.40  
  7 purchase totals = $753.89       $809.6353   $809.64   $809.60   $809.60