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 $84.59   11.611%   $94.4117   $94.41   $94.40   $94.40  
  Purchase #2 $216.88   9.300%   $237.0498   $237.05   $237.05   $237.00  
  Purchase #3 $59.55   3.469%   $61.6158   $61.62   $61.60   $61.60  
  Purchase #4 $97.74   6.716%   $104.3042   $104.30   $104.30   $104.30  
  Purchase #5 $232.78   3.125%   $240.0544   $240.05   $240.05   $240.10  
  Purchase #6 $81.57   5.297%   $85.8908   $85.89   $85.90   $85.90  
  Purchase #7 $228.57   6.292%   $242.9516   $242.95   $242.95   $243.00  
  7 purchase totals = $1,001.68       $1,066.2783   $1,066.27   $1,066.25   $1,066.30