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 $212.34   7.496%   $228.257   $228.26   $228.25   $228.30  
  Purchase #2 $205.47   8.611%   $223.163   $223.16   $223.15   $223.20  
  Purchase #3 $121.37   3.783%   $125.9614   $125.96   $125.95   $126.00  
  Purchase #4 $126.43   11.781%   $141.3247   $141.32   $141.30   $141.30  
  Purchase #5 $160.29   5.169%   $168.5754   $168.58   $168.60   $168.60  
  Purchase #6 $201.91   6.243%   $214.5152   $214.52   $214.50   $214.50  
  Purchase #7 $22.25   7.677%   $23.9581   $23.96   $23.95   $24.00  
  7 purchase totals = $1,050.06       $1,125.7548   $1,125.76   $1,125.70   $1,125.90