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 $66.79   4.200%   $69.5952   $69.60   $69.60   $69.60  
  Purchase #2 $108.68   12.814%   $122.6063   $122.61   $122.60   $122.60  
  Purchase #3 $167.26   5.770%   $176.9109   $176.91   $176.90   $176.90  
  Purchase #4 $203.26   7.126%   $217.7443   $217.74   $217.75   $217.70  
  Purchase #5 $152.55   12.754%   $172.0062   $172.01   $172.00   $172.00  
  Purchase #6 $36.47   6.455%   $38.8241   $38.82   $38.80   $38.80  
  Purchase #7 $27.85   6.231%   $29.5853   $29.59   $29.60   $29.60  
  7 purchase totals = $762.86       $827.2723   $827.28   $827.25   $827.20