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 $44.99   10.210%   $49.5835   $49.58   $49.60   $49.60  
  Purchase #2 $179.65   13.350%   $203.6333   $203.63   $203.65   $203.60  
  Purchase #3 $173.36   7.797%   $186.8769   $186.88   $186.90   $186.90  
  Purchase #4 $133.98   6.191%   $142.2747   $142.27   $142.25   $142.30  
  Purchase #5 $193.95   6.298%   $206.165   $206.17   $206.15   $206.20  
  Purchase #6 $216.59   13.155%   $245.0824   $245.08   $245.10   $245.10  
  Purchase #7 $186.45   13.788%   $212.1577   $212.16   $212.15   $212.20  
  7 purchase totals = $1,128.97       $1,245.7735   $1,245.77   $1,245.80   $1,245.90