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 $232.88   12.348%   $261.636   $261.64   $261.65   $261.60  
  Purchase #2 $122.36   11.664%   $136.6321   $136.63   $136.65   $136.60  
  Purchase #3 $73.44   4.284%   $76.5862   $76.59   $76.60   $76.60  
  Purchase #4 $190.35   13.290%   $215.6475   $215.65   $215.65   $215.60  
  Purchase #5 $27.52   12.421%   $30.9383   $30.94   $30.95   $30.90  
  Purchase #6 $128.90   4.179%   $134.2867   $134.29   $134.30   $134.30  
  Purchase #7 $194.28   5.415%   $204.8003   $204.80   $204.80   $204.80  
  7 purchase totals = $969.73       $1,060.5271   $1,060.54   $1,060.60   $1,060.40