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 $84.90   12.654%   $95.6432   $95.64   $95.65   $95.60  
  Purchase #2 $194.88   4.673%   $203.9867   $203.99   $204.00   $204.00  
  Purchase #3 $61.62   7.131%   $66.0141   $66.01   $66.00   $66.00  
  Purchase #4 $176.39   12.252%   $198.0013   $198.00   $198.00   $198.00  
  Purchase #5 $130.83   4.780%   $137.0837   $137.08   $137.10   $137.10  
  Purchase #6 $210.93   5.712%   $222.9783   $222.98   $223.00   $223.00  
  Purchase #7 $249.79   10.226%   $275.3335   $275.33   $275.35   $275.30  
  7 purchase totals = $1,109.34       $1,199.0408   $1,199.03   $1,199.10   $1,199.00