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 $233.75   13.811%   $266.0332   $266.03   $266.05   $266.00  
  Purchase #2 $82.73   7.530%   $88.9596   $88.96   $88.95   $89.00  
  Purchase #3 $128.93   12.596%   $145.17   $145.17   $145.15   $145.20  
  Purchase #4 $213.32   9.819%   $234.2659   $234.27   $234.25   $234.30  
  Purchase #5 $47.37   7.182%   $50.7721   $50.77   $50.75   $50.80  
  Purchase #6 $176.35   8.786%   $191.8441   $191.84   $191.85   $191.80  
  Purchase #7 $242.47   5.432%   $255.641   $255.64   $255.65   $255.60  
  7 purchase totals = $1,124.92       $1,232.6859   $1,232.68   $1,232.65   $1,232.70