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 $181.74   7.717%   $195.7649   $195.76   $195.75   $195.80  
  Purchase #2 $183.25   9.153%   $200.0229   $200.02   $200.00   $200.00  
  Purchase #3 $113.87   8.240%   $123.2529   $123.25   $123.25   $123.30  
  Purchase #4 $238.49   9.332%   $260.7459   $260.75   $260.75   $260.70  
  Purchase #5 $128.61   6.717%   $137.2487   $137.25   $137.25   $137.20  
  Purchase #6 $125.40   3.591%   $129.9031   $129.90   $129.90   $129.90  
  Purchase #7 $212.36   4.427%   $221.7612   $221.76   $221.75   $221.80  
  7 purchase totals = $1,183.72       $1,268.6996   $1,268.69   $1,268.65   $1,268.70