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 $67.66   12.608%   $76.1906   $76.19   $76.20   $76.20  
  Purchase #2 $227.87   7.744%   $245.5163   $245.52   $245.50   $245.50  
  Purchase #3 $137.66   10.672%   $152.3511   $152.35   $152.35   $152.40  
  Purchase #4 $98.48   8.539%   $106.8892   $106.89   $106.90   $106.90  
  Purchase #5 $14.60   12.826%   $16.4726   $16.47   $16.45   $16.50  
  Purchase #6 $195.74   10.592%   $216.4728   $216.47   $216.45   $216.50  
  Purchase #7 $160.87   6.642%   $171.555   $171.56   $171.55   $171.60  
  7 purchase totals = $902.88       $985.4476   $985.45   $985.40   $985.60