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 $173.77   7.486%   $186.7784   $186.78   $186.80   $186.80  
  Purchase #2 $92.49   6.653%   $98.6434   $98.64   $98.65   $98.60  
  Purchase #3 $182.26   4.194%   $189.904   $189.90   $189.90   $189.90  
  Purchase #4 $147.38   9.657%   $161.6125   $161.61   $161.60   $161.60  
  Purchase #5 $79.40   9.395%   $86.8596   $86.86   $86.85   $86.90  
  Purchase #6 $247.30   11.327%   $275.3117   $275.31   $275.30   $275.30  
  Purchase #7 $6.42   8.196%   $6.9462   $6.95   $6.95   $6.90  
  7 purchase totals = $929.02       $1,006.0558   $1,006.05   $1,006.05   $1,006.00