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 $55.52   11.765%   $62.0519   $62.05   $62.05   $62.10  
  Purchase #2 $213.26   8.327%   $231.0182   $231.02   $231.00   $231.00  
  Purchase #3 $230.35   4.137%   $239.8796   $239.88   $239.90   $239.90  
  Purchase #4 $215.86   9.826%   $237.0704   $237.07   $237.05   $237.10  
  Purchase #5 $75.26   8.430%   $81.6044   $81.60   $81.60   $81.60  
  Purchase #6 $14.74   11.550%   $16.4425   $16.44   $16.45   $16.40  
  Purchase #7 $135.81   11.288%   $151.1402   $151.14   $151.15   $151.10  
  7 purchase totals = $940.80       $1,019.2072   $1,019.20   $1,019.20   $1,019.20