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 $73.97   13.569%   $84.007   $84.01   $84.00   $84.00  
  Purchase #2 $119.33   11.134%   $132.6162   $132.62   $132.60   $132.60  
  Purchase #3 $206.93   8.682%   $224.8957   $224.90   $224.90   $224.90  
  Purchase #4 $235.36   11.691%   $262.8759   $262.88   $262.90   $262.90  
  Purchase #5 $176.34   7.286%   $189.1881   $189.19   $189.20   $189.20  
  Purchase #6 $101.66   5.331%   $107.0795   $107.08   $107.10   $107.10  
  Purchase #7 $116.95   6.135%   $124.1249   $124.12   $124.10   $124.10  
  7 purchase totals = $1,030.54       $1,124.7873   $1,124.80   $1,124.80   $1,124.80