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 $236.97   9.723%   $260.0106   $260.01   $260.00   $260.00  
  Purchase #2 $77.42   10.678%   $85.6869   $85.69   $85.70   $85.70  
  Purchase #3 $20.72   8.665%   $22.5154   $22.52   $22.50   $22.50  
  Purchase #4 $61.42   13.550%   $69.7424   $69.74   $69.75   $69.70  
  Purchase #5 $246.38   4.517%   $257.509   $257.51   $257.50   $257.50  
  Purchase #6 $150.74   7.715%   $162.3696   $162.37   $162.35   $162.40  
  Purchase #7 $194.37   5.325%   $204.7202   $204.72   $204.70   $204.70  
  7 purchase totals = $988.02       $1,062.5541   $1,062.56   $1,062.50   $1,062.50