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 $238.74   9.572%   $261.5922   $261.59   $261.60   $261.60  
  Purchase #2 $141.92   13.809%   $161.5177   $161.52   $161.50   $161.50  
  Purchase #3 $249.62   6.596%   $266.0849   $266.08   $266.10   $266.10  
  Purchase #4 $208.72   9.645%   $228.851   $228.85   $228.85   $228.90  
  Purchase #5 $14.93   13.496%   $16.945   $16.95   $16.95   $16.90  
  Purchase #6 $82.71   10.184%   $91.1332   $91.13   $91.15   $91.10  
  Purchase #7 $172.71   8.839%   $187.9758   $187.98   $188.00   $188.00  
  7 purchase totals = $1,109.35       $1,214.0998   $1,214.10   $1,214.15   $1,214.10