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 $192.53   8.600%   $209.0876   $209.09   $209.10   $209.10  
  Purchase #2 $131.43   6.530%   $140.0124   $140.01   $140.00   $140.00  
  Purchase #3 $43.42   12.657%   $48.9157   $48.92   $48.90   $48.90  
  Purchase #4 $226.59   9.441%   $247.9824   $247.98   $248.00   $248.00  
  Purchase #5 $145.55   6.607%   $155.1665   $155.17   $155.15   $155.20  
  Purchase #6 $220.77   12.335%   $248.002   $248.00   $248.00   $248.00  
  Purchase #7 $146.98   3.840%   $152.624   $152.62   $152.60   $152.60  
  7 purchase totals = $1,107.27       $1,201.7906   $1,201.79   $1,201.75   $1,201.80