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 $68.96   11.824%   $77.1138   $77.11   $77.10   $77.10  
  Purchase #2 $214.28   5.631%   $226.3461   $226.35   $226.35   $226.30  
  Purchase #3 $230.63   8.864%   $251.073   $251.07   $251.05   $251.10  
  Purchase #4 $85.81   12.295%   $96.3603   $96.36   $96.35   $96.40  
  Purchase #5 $184.84   5.222%   $194.4923   $194.49   $194.50   $194.50  
  Purchase #6 $202.34   11.321%   $225.2469   $225.25   $225.25   $225.20  
  Purchase #7 $138.87   4.303%   $144.8456   $144.85   $144.85   $144.80  
  7 purchase totals = $1,125.73       $1,215.4780   $1,215.48   $1,215.45   $1,215.40