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 $238.26   5.462%   $251.2738   $251.27   $251.25   $251.30  
  Purchase #2 $236.57   8.184%   $255.9309   $255.93   $255.95   $255.90  
  Purchase #3 $184.46   10.390%   $203.6254   $203.63   $203.65   $203.60  
  Purchase #4 $52.28   8.584%   $56.7677   $56.77   $56.75   $56.80  
  Purchase #5 $237.94   3.621%   $246.5558   $246.56   $246.55   $246.60  
  Purchase #6 $142.44   6.352%   $151.4878   $151.49   $151.50   $151.50  
  Purchase #7 $200.88   5.345%   $211.617   $211.62   $211.60   $211.60  
  7 purchase totals = $1,292.83       $1,377.2584   $1,377.27   $1,377.25   $1,377.30