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 $62.44   11.261%   $69.4714   $69.47   $69.45   $69.50  
  Purchase #2 $58.65   9.691%   $64.3338   $64.33   $64.35   $64.30  
  Purchase #3 $87.73   13.305%   $99.4025   $99.40   $99.40   $99.40  
  Purchase #4 $184.75   8.151%   $199.809   $199.81   $199.80   $199.80  
  Purchase #5 $248.35   10.442%   $274.2827   $274.28   $274.30   $274.30  
  Purchase #6 $124.82   5.219%   $131.3344   $131.33   $131.35   $131.30  
  Purchase #7 $103.95   4.831%   $108.9718   $108.97   $108.95   $109.00  
  7 purchase totals = $870.69       $947.6056   $947.59   $947.60   $947.60