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 $214.29   4.759%   $224.4881   $224.49   $224.50   $224.50  
  Purchase #2 $224.63   10.233%   $247.6164   $247.62   $247.60   $247.60  
  Purchase #3 $24.29   13.492%   $27.5672   $27.57   $27.55   $27.60  
  Purchase #4 $188.39   4.751%   $197.3404   $197.34   $197.35   $197.30  
  Purchase #5 $131.32   13.665%   $149.2649   $149.26   $149.25   $149.30  
  Purchase #6 $65.97   11.609%   $73.6285   $73.63   $73.65   $73.60  
  Purchase #7 $223.64   10.415%   $246.9321   $246.93   $246.95   $246.90  
  7 purchase totals = $1,072.53       $1,166.8376   $1,166.84   $1,166.85   $1,166.80