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 $91.89   8.395%   $99.6042   $99.60   $99.60   $99.60  
  Purchase #2 $207.41   13.757%   $235.9434   $235.94   $235.95   $235.90  
  Purchase #3 $172.89   12.155%   $193.9048   $193.90   $193.90   $193.90  
  Purchase #4 $205.41   11.699%   $229.4409   $229.44   $229.45   $229.40  
  Purchase #5 $120.88   6.453%   $128.6804   $128.68   $128.70   $128.70  
  Purchase #6 $174.90   6.186%   $185.7193   $185.72   $185.70   $185.70  
  Purchase #7 $109.47   11.505%   $122.0645   $122.06   $122.05   $122.10  
  7 purchase totals = $1,082.85       $1,195.3575   $1,195.34   $1,195.35   $1,195.30