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 $213.94   8.579%   $232.2939   $232.29   $232.30   $232.30  
  Purchase #2 $17.51   9.379%   $19.1523   $19.15   $19.15   $19.20  
  Purchase #3 $117.25   12.773%   $132.2263   $132.23   $132.25   $132.20  
  Purchase #4 $212.66   4.788%   $222.8422   $222.84   $222.85   $222.80  
  Purchase #5 $130.32   9.606%   $142.8385   $142.84   $142.85   $142.80  
  Purchase #6 $142.43   5.553%   $150.3391   $150.34   $150.35   $150.30  
  Purchase #7 $130.36   3.493%   $134.9135   $134.91   $134.90   $134.90  
  7 purchase totals = $964.47       $1,034.6058   $1,034.60   $1,034.65   $1,034.50