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 $33.97   8.124%   $36.7297   $36.73   $36.75   $36.70  
  Purchase #2 $150.53   6.866%   $160.8654   $160.87   $160.85   $160.90  
  Purchase #3 $162.61   11.827%   $181.8419   $181.84   $181.85   $181.80  
  Purchase #4 $176.35   12.613%   $198.593   $198.59   $198.60   $198.60  
  Purchase #5 $83.97   6.856%   $89.727   $89.73   $89.75   $89.70  
  Purchase #6 $54.74   6.130%   $58.0956   $58.10   $58.10   $58.10  
  Purchase #7 $147.32   13.398%   $167.0579   $167.06   $167.05   $167.10  
  7 purchase totals = $809.49       $892.9105   $892.92   $892.95   $892.90