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 $58.59   4.118%   $61.0027   $61.00   $61.00   $61.00  
  Purchase #2 $64.93   11.202%   $72.2035   $72.20   $72.20   $72.20  
  Purchase #3 $25.44   8.759%   $27.6683   $27.67   $27.65   $27.70  
  Purchase #4 $77.26   4.494%   $80.7321   $80.73   $80.75   $80.70  
  Purchase #5 $236.90   9.170%   $258.6237   $258.62   $258.60   $258.60  
  Purchase #6 $15.99   7.488%   $17.1873   $17.19   $17.20   $17.20  
  Purchase #7 $125.46   6.295%   $133.3577   $133.36   $133.35   $133.40  
  7 purchase totals = $604.57       $650.7753   $650.77   $650.75   $650.80