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 $204.89   5.574%   $216.3106   $216.31   $216.30   $216.30  
  Purchase #2 $7.43   12.239%   $8.3394   $8.34   $8.35   $8.30  
  Purchase #3 $55.84   5.136%   $58.7079   $58.71   $58.70   $58.70  
  Purchase #4 $26.63   9.652%   $29.2003   $29.20   $29.20   $29.20  
  Purchase #5 $203.76   7.379%   $218.7955   $218.80   $218.80   $218.80  
  Purchase #6 $60.54   7.707%   $65.2058   $65.21   $65.20   $65.20  
  Purchase #7 $213.90   9.302%   $233.797   $233.80   $233.80   $233.80  
  7 purchase totals = $772.99       $830.3565   $830.37   $830.35   $830.30