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 $71.56   4.371%   $74.6879   $74.69   $74.70   $74.70  
  Purchase #2 $100.29   6.162%   $106.4699   $106.47   $106.45   $106.50  
  Purchase #3 $176.81   4.562%   $184.8761   $184.88   $184.90   $184.90  
  Purchase #4 $72.36   6.860%   $77.3239   $77.32   $77.30   $77.30  
  Purchase #5 $218.95   12.382%   $246.0604   $246.06   $246.05   $246.10  
  Purchase #6 $140.87   13.677%   $160.1368   $160.14   $160.15   $160.10  
  Purchase #7 $103.59   9.837%   $113.7801   $113.78   $113.80   $113.80  
  7 purchase totals = $884.43       $963.3351   $963.34   $963.35   $963.40