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 $58.96   8.131%   $63.754   $63.75   $63.75   $63.80  
  Purchase #2 $140.68   3.750%   $145.9555   $145.96   $145.95   $146.00  
  Purchase #3 $224.35   7.212%   $240.5301   $240.53   $240.55   $240.50  
  Purchase #4 $143.26   6.476%   $152.5375   $152.54   $152.55   $152.50  
  Purchase #5 $197.36   13.251%   $223.5122   $223.51   $223.50   $223.50  
  Purchase #6 $164.30   12.380%   $184.6403   $184.64   $184.65   $184.60  
  Purchase #7 $59.59   12.211%   $66.8665   $66.87   $66.85   $66.90  
  7 purchase totals = $988.50       $1,077.7961   $1,077.80   $1,077.80   $1,077.80