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 $244.87   8.277%   $265.1379   $265.14   $265.15   $265.10  
  Purchase #2 $145.93   7.561%   $156.9638   $156.96   $156.95   $157.00  
  Purchase #3 $38.75   7.559%   $41.6791   $41.68   $41.70   $41.70  
  Purchase #4 $79.49   4.379%   $82.9709   $82.97   $82.95   $83.00  
  Purchase #5 $231.49   5.818%   $244.9581   $244.96   $244.95   $245.00  
  Purchase #6 $231.99   4.731%   $242.9654   $242.97   $242.95   $243.00  
  Purchase #7 $66.95   9.741%   $73.4716   $73.47   $73.45   $73.50  
  7 purchase totals = $1,039.47       $1,108.1468   $1,108.15   $1,108.10   $1,108.30