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 $78.54   5.552%   $82.9005   $82.90   $82.90   $82.90  
  Purchase #2 $211.46   11.395%   $235.5559   $235.56   $235.55   $235.60  
  Purchase #3 $241.70   11.430%   $269.3263   $269.33   $269.35   $269.30  
  Purchase #4 $46.29   8.219%   $50.0946   $50.09   $50.10   $50.10  
  Purchase #5 $25.38   4.186%   $26.4424   $26.44   $26.45   $26.40  
  Purchase #6 $223.30   5.769%   $236.1822   $236.18   $236.20   $236.20  
  Purchase #7 $117.25   12.794%   $132.251   $132.25   $132.25   $132.30  
  7 purchase totals = $943.92       $1,032.7529   $1,032.75   $1,032.80   $1,032.80