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 $165.99   11.597%   $185.2399   $185.24   $185.25   $185.20  
  Purchase #2 $191.73   13.650%   $217.9011   $217.90   $217.90   $217.90  
  Purchase #3 $120.64   5.307%   $127.0424   $127.04   $127.05   $127.00  
  Purchase #4 $9.80   5.738%   $10.3623   $10.36   $10.35   $10.40  
  Purchase #5 $124.42   6.470%   $132.47   $132.47   $132.45   $132.50  
  Purchase #6 $228.50   6.203%   $242.6739   $242.67   $242.65   $242.70  
  Purchase #7 $128.78   6.826%   $137.5705   $137.57   $137.55   $137.60  
  7 purchase totals = $969.86       $1,053.2601   $1,053.25   $1,053.20   $1,053.30