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 $213.52   10.257%   $235.4207   $235.42   $235.40   $235.40  
  Purchase #2 $22.89   12.248%   $25.6936   $25.69   $25.70   $25.70  
  Purchase #3 $162.45   10.617%   $179.6973   $179.70   $179.70   $179.70  
  Purchase #4 $27.86   7.312%   $29.8971   $29.90   $29.90   $29.90  
  Purchase #5 $83.91   9.201%   $91.6306   $91.63   $91.65   $91.60  
  Purchase #6 $18.59   9.573%   $20.3696   $20.37   $20.35   $20.40  
  Purchase #7 $229.63   5.816%   $242.9853   $242.99   $243.00   $243.00  
  7 purchase totals = $758.85       $825.6942   $825.70   $825.70   $825.70