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 $218.99   12.751%   $246.9134   $246.91   $246.90   $246.90  
  Purchase #2 $118.27   3.606%   $122.5348   $122.53   $122.55   $122.50  
  Purchase #3 $214.88   13.378%   $243.6266   $243.63   $243.65   $243.60  
  Purchase #4 $178.55   7.299%   $191.5824   $191.58   $191.60   $191.60  
  Purchase #5 $20.80   7.384%   $22.3359   $22.34   $22.35   $22.30  
  Purchase #6 $165.33   11.198%   $183.8437   $183.84   $183.85   $183.80  
  Purchase #7 $11.42   10.706%   $12.6426   $12.64   $12.65   $12.60  
  7 purchase totals = $928.24       $1,023.4794   $1,023.47   $1,023.55   $1,023.30