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 $208.65   11.820%   $233.3124   $233.31   $233.30   $233.30  
  Purchase #2 $36.88   13.224%   $41.757   $41.76   $41.75   $41.80  
  Purchase #3 $162.84   11.173%   $181.0341   $181.03   $181.05   $181.00  
  Purchase #4 $132.98   6.574%   $141.7221   $141.72   $141.70   $141.70  
  Purchase #5 $130.55   6.393%   $138.8961   $138.90   $138.90   $138.90  
  Purchase #6 $174.39   9.658%   $191.2326   $191.23   $191.25   $191.20  
  Purchase #7 $15.86   4.641%   $16.5961   $16.60   $16.60   $16.60  
  7 purchase totals = $862.15       $944.5504   $944.55   $944.55   $944.50