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 $238.45   10.240%   $262.8673   $262.87   $262.85   $262.90  
  Purchase #2 $125.27   8.324%   $135.6975   $135.70   $135.70   $135.70  
  Purchase #3 $200.27   4.395%   $209.0719   $209.07   $209.05   $209.10  
  Purchase #4 $161.44   12.581%   $181.7508   $181.75   $181.75   $181.80  
  Purchase #5 $216.96   3.509%   $224.5731   $224.57   $224.55   $224.60  
  Purchase #6 $128.78   4.198%   $134.1862   $134.19   $134.20   $134.20  
  Purchase #7 $205.57   3.217%   $212.1832   $212.18   $212.20   $212.20  
  7 purchase totals = $1,276.74       $1,360.3300   $1,360.33   $1,360.30   $1,360.50