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 $57.46   5.322%   $60.518   $60.52   $60.50   $60.50  
  Purchase #2 $100.26   5.319%   $105.5928   $105.59   $105.60   $105.60  
  Purchase #3 $222.51   11.338%   $247.7382   $247.74   $247.75   $247.70  
  Purchase #4 $102.40   13.249%   $115.967   $115.97   $115.95   $116.00  
  Purchase #5 $13.97   8.813%   $15.2012   $15.20   $15.20   $15.20  
  Purchase #6 $192.47   12.311%   $216.165   $216.17   $216.15   $216.20  
  Purchase #7 $9.81   5.535%   $10.353   $10.35   $10.35   $10.40  
  7 purchase totals = $698.88       $771.5352   $771.54   $771.50   $771.60