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 $6.46   4.836%   $6.7724   $6.77   $6.75   $6.80  
  Purchase #2 $5.72   4.175%   $5.9588   $5.96   $5.95   $6.00  
  Purchase #3 $27.43   5.189%   $28.8533   $28.85   $28.85   $28.90  
  Purchase #4 $123.42   8.255%   $133.6083   $133.61   $133.60   $133.60  
  Purchase #5 $31.99   10.450%   $35.333   $35.33   $35.35   $35.30  
  Purchase #6 $165.84   6.625%   $176.8269   $176.83   $176.85   $176.80  
  Purchase #7 $92.71   7.374%   $99.5464   $99.55   $99.55   $99.50  
  7 purchase totals = $453.57       $486.8991   $486.90   $486.90   $486.90