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 $235.88   9.337%   $257.9041   $257.90   $257.90   $257.90  
  Purchase #2 $208.93   9.437%   $228.6467   $228.65   $228.65   $228.60  
  Purchase #3 $66.61   11.703%   $74.4054   $74.41   $74.40   $74.40  
  Purchase #4 $142.97   10.725%   $158.3035   $158.30   $158.30   $158.30  
  Purchase #5 $75.38   12.513%   $84.8123   $84.81   $84.80   $84.80  
  Purchase #6 $102.73   7.848%   $110.7923   $110.79   $110.80   $110.80  
  Purchase #7 $97.31   9.167%   $106.2304   $106.23   $106.25   $106.20  
  7 purchase totals = $929.81       $1,021.0947   $1,021.09   $1,021.10   $1,021.00