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 $206.66   11.440%   $230.3019   $230.30   $230.30   $230.30  
  Purchase #2 $116.84   9.844%   $128.3417   $128.34   $128.35   $128.30  
  Purchase #3 $82.54   4.553%   $86.298   $86.30   $86.30   $86.30  
  Purchase #4 $135.50   12.209%   $152.0432   $152.04   $152.05   $152.00  
  Purchase #5 $43.70   6.607%   $46.5873   $46.59   $46.60   $46.60  
  Purchase #6 $102.38   4.661%   $107.1519   $107.15   $107.15   $107.20  
  Purchase #7 $99.72   4.625%   $104.3321   $104.33   $104.35   $104.30  
  7 purchase totals = $787.34       $855.0561   $855.05   $855.10   $855.00