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 $194.52   4.463%   $203.2014   $203.20   $203.20   $203.20  
  Purchase #2 $62.62   5.260%   $65.9138   $65.91   $65.90   $65.90  
  Purchase #3 $77.88   3.339%   $80.4804   $80.48   $80.50   $80.50  
  Purchase #4 $16.63   3.359%   $17.1886   $17.19   $17.20   $17.20  
  Purchase #5 $98.35   13.410%   $111.5387   $111.54   $111.55   $111.50  
  Purchase #6 $194.58   3.172%   $200.7521   $200.75   $200.75   $200.80  
  Purchase #7 $130.63   5.507%   $137.8238   $137.82   $137.80   $137.80  
  7 purchase totals = $775.21       $816.8988   $816.89   $816.90   $816.90