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 $212.70   10.478%   $234.9867   $234.99   $235.00   $235.00  
  Purchase #2 $146.38   12.483%   $164.6526   $164.65   $164.65   $164.70  
  Purchase #3 $125.66   9.153%   $137.1617   $137.16   $137.15   $137.20  
  Purchase #4 $138.94   4.591%   $145.3187   $145.32   $145.30   $145.30  
  Purchase #5 $11.53   6.107%   $12.2341   $12.23   $12.25   $12.20  
  Purchase #6 $75.54   9.707%   $82.8727   $82.87   $82.85   $82.90  
  Purchase #7 $206.73   9.847%   $227.0867   $227.09   $227.10   $227.10  
  7 purchase totals = $917.48       $1,004.3132   $1,004.31   $1,004.30   $1,004.40