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 $246.47   8.545%   $267.5309   $267.53   $267.55   $267.50  
  Purchase #2 $92.29   3.108%   $95.1584   $95.16   $95.15   $95.20  
  Purchase #3 $123.87   3.492%   $128.1955   $128.20   $128.20   $128.20  
  Purchase #4 $36.56   8.838%   $39.7912   $39.79   $39.80   $39.80  
  Purchase #5 $124.25   8.501%   $134.8125   $134.81   $134.80   $134.80  
  Purchase #6 $180.44   12.396%   $202.8073   $202.81   $202.80   $202.80  
  Purchase #7 $74.30   13.762%   $84.5252   $84.53   $84.55   $84.50  
  7 purchase totals = $878.18       $952.8210   $952.83   $952.85   $952.80