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 $146.87   13.544%   $166.7621   $166.76   $166.75   $166.80  
  Purchase #2 $71.94   7.288%   $77.183   $77.18   $77.20   $77.20  
  Purchase #3 $162.32   8.471%   $176.0701   $176.07   $176.05   $176.10  
  Purchase #4 $250.52   4.194%   $261.0268   $261.03   $261.05   $261.00  
  Purchase #5 $197.34   11.259%   $219.5585   $219.56   $219.55   $219.60  
  Purchase #6 $163.85   5.869%   $173.4664   $173.47   $173.45   $173.50  
  Purchase #7 $148.76   9.395%   $162.736   $162.74   $162.75   $162.70  
  7 purchase totals = $1,141.60       $1,236.8029   $1,236.81   $1,236.80   $1,236.90