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 $188.27   9.612%   $206.3665   $206.37   $206.35   $206.40  
  Purchase #2 $179.61   8.477%   $194.8355   $194.84   $194.85   $194.80  
  Purchase #3 $161.81   6.279%   $171.97   $171.97   $171.95   $172.00  
  Purchase #4 $54.39   10.237%   $59.9579   $59.96   $59.95   $60.00  
  Purchase #5 $159.82   11.732%   $178.5701   $178.57   $178.55   $178.60  
  Purchase #6 $248.53   5.822%   $262.9994   $263.00   $263.00   $263.00  
  Purchase #7 $140.37   10.657%   $155.3292   $155.33   $155.35   $155.30  
  7 purchase totals = $1,132.80       $1,230.0286   $1,230.04   $1,230.00   $1,230.10