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 $162.81   10.382%   $179.7129   $179.71   $179.70   $179.70  
  Purchase #2 $239.70   12.747%   $270.2546   $270.25   $270.25   $270.30  
  Purchase #3 $59.28   9.378%   $64.8393   $64.84   $64.85   $64.80  
  Purchase #4 $65.42   11.558%   $72.9812   $72.98   $73.00   $73.00  
  Purchase #5 $235.64   11.586%   $262.9413   $262.94   $262.95   $262.90  
  Purchase #6 $60.82   7.394%   $65.317   $65.32   $65.30   $65.30  
  Purchase #7 $27.60   11.504%   $30.7751   $30.78   $30.80   $30.80  
  7 purchase totals = $851.27       $946.8214   $946.82   $946.85   $946.80