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 $43.50   5.390%   $45.8447   $45.84   $45.85   $45.80  
  Purchase #2 $21.97   13.708%   $24.9816   $24.98   $25.00   $25.00  
  Purchase #3 $76.31   7.310%   $81.8883   $81.89   $81.90   $81.90  
  Purchase #4 $127.99   10.603%   $141.5608   $141.56   $141.55   $141.60  
  Purchase #5 $204.28   4.563%   $213.6013   $213.60   $213.60   $213.60  
  Purchase #6 $57.63   6.169%   $61.1852   $61.19   $61.20   $61.20  
  Purchase #7 $108.53   11.228%   $120.7157   $120.72   $120.70   $120.70  
  7 purchase totals = $640.21       $689.7776   $689.78   $689.80   $689.80