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 $86.90   8.211%   $94.0354   $94.04   $94.05   $94.00  
  Purchase #2 $177.37   12.338%   $199.2539   $199.25   $199.25   $199.30  
  Purchase #3 $238.86   8.608%   $259.4211   $259.42   $259.40   $259.40  
  Purchase #4 $211.62   5.319%   $222.8761   $222.88   $222.90   $222.90  
  Purchase #5 $114.25   11.144%   $126.982   $126.98   $127.00   $127.00  
  Purchase #6 $101.84   4.516%   $106.4391   $106.44   $106.45   $106.40  
  Purchase #7 $108.42   13.457%   $123.0101   $123.01   $123.00   $123.00  
  7 purchase totals = $1,039.26       $1,132.0177   $1,132.02   $1,132.05   $1,132.00