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 $57.94   5.206%   $60.9564   $60.96   $60.95   $61.00  
  Purchase #2 $215.40   5.402%   $227.0359   $227.04   $227.05   $227.00  
  Purchase #3 $72.73   12.411%   $81.7565   $81.76   $81.75   $81.80  
  Purchase #4 $248.48   9.554%   $272.2198   $272.22   $272.20   $272.20  
  Purchase #5 $228.96   10.317%   $252.5818   $252.58   $252.60   $252.60  
  Purchase #6 $144.45   11.382%   $160.8913   $160.89   $160.90   $160.90  
  Purchase #7 $51.56   13.797%   $58.6737   $58.67   $58.65   $58.70  
  7 purchase totals = $1,019.52       $1,114.1154   $1,114.12   $1,114.10   $1,114.20