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 $55.56   10.137%   $61.1921   $61.19   $61.20   $61.20  
  Purchase #2 $57.74   11.718%   $64.506   $64.51   $64.50   $64.50  
  Purchase #3 $56.64   7.821%   $61.0698   $61.07   $61.05   $61.10  
  Purchase #4 $18.87   13.757%   $21.4659   $21.47   $21.45   $21.50  
  Purchase #5 $236.78   9.245%   $258.6703   $258.67   $258.65   $258.70  
  Purchase #6 $231.69   11.196%   $257.63   $257.63   $257.65   $257.60  
  Purchase #7 $160.47   4.500%   $167.6912   $167.69   $167.70   $167.70  
  7 purchase totals = $817.75       $892.2253   $892.23   $892.20   $892.30