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 $209.84   12.108%   $235.2474   $235.25   $235.25   $235.20  
  Purchase #2 $89.97   9.679%   $98.6782   $98.68   $98.70   $98.70  
  Purchase #3 $163.65   6.742%   $174.6833   $174.68   $174.70   $174.70  
  Purchase #4 $42.77   10.133%   $47.1039   $47.10   $47.10   $47.10  
  Purchase #5 $18.95   11.228%   $21.0777   $21.08   $21.10   $21.10  
  Purchase #6 $162.77   11.553%   $181.5748   $181.57   $181.55   $181.60  
  Purchase #7 $13.64   6.836%   $14.5724   $14.57   $14.55   $14.60  
  7 purchase totals = $701.59       $772.9377   $772.93   $772.95   $773.00