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 $153.76   7.644%   $165.5134   $165.51   $165.50   $165.50  
  Purchase #2 $198.93   6.293%   $211.4487   $211.45   $211.45   $211.40  
  Purchase #3 $25.26   13.271%   $28.6123   $28.61   $28.60   $28.60  
  Purchase #4 $247.63   6.143%   $262.8419   $262.84   $262.85   $262.80  
  Purchase #5 $32.25   8.483%   $34.9858   $34.99   $35.00   $35.00  
  Purchase #6 $81.35   5.665%   $85.9585   $85.96   $85.95   $86.00  
  Purchase #7 $194.46   5.658%   $205.4625   $205.46   $205.45   $205.50  
  7 purchase totals = $933.64       $994.8231   $994.82   $994.80   $994.80