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 $212.82   3.353%   $219.9559   $219.96   $219.95   $220.00  
  Purchase #2 $97.47   5.392%   $102.7256   $102.73   $102.75   $102.70  
  Purchase #3 $105.47   4.185%   $109.8839   $109.88   $109.90   $109.90  
  Purchase #4 $119.60   4.704%   $125.226   $125.23   $125.25   $125.20  
  Purchase #5 $248.87   7.224%   $266.8484   $266.85   $266.85   $266.80  
  Purchase #6 $119.86   5.681%   $126.6692   $126.67   $126.65   $126.70  
  Purchase #7 $226.52   6.832%   $241.9958   $242.00   $242.00   $242.00  
  7 purchase totals = $1,130.61       $1,193.3048   $1,193.32   $1,193.35   $1,193.30