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 $22.95   6.308%   $24.3977   $24.40   $24.40   $24.40  
  Purchase #2 $54.75   5.376%   $57.6934   $57.69   $57.70   $57.70  
  Purchase #3 $192.26   10.548%   $212.5396   $212.54   $212.55   $212.50  
  Purchase #4 $138.52   6.484%   $147.5016   $147.50   $147.50   $147.50  
  Purchase #5 $46.42   11.794%   $51.8948   $51.89   $51.90   $51.90  
  Purchase #6 $206.70   3.803%   $214.5608   $214.56   $214.55   $214.60  
  Purchase #7 $197.93   10.652%   $219.0135   $219.01   $219.00   $219.00  
  7 purchase totals = $859.53       $927.6014   $927.59   $927.60   $927.60