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 $210.92   7.504%   $226.7474   $226.75   $226.75   $226.70  
  Purchase #2 $121.61   13.745%   $138.3253   $138.33   $138.35   $138.30  
  Purchase #3 $14.60   10.844%   $16.1832   $16.18   $16.20   $16.20  
  Purchase #4 $144.50   11.784%   $161.5279   $161.53   $161.55   $161.50  
  Purchase #5 $227.51   6.374%   $242.0115   $242.01   $242.00   $242.00  
  Purchase #6 $176.49   6.433%   $187.8436   $187.84   $187.85   $187.80  
  Purchase #7 $38.45   9.200%   $41.9874   $41.99   $42.00   $42.00  
  7 purchase totals = $934.08       $1,014.6263   $1,014.63   $1,014.70   $1,014.50