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 $56.55   9.376%   $61.8521   $61.85   $61.85   $61.90  
  Purchase #2 $138.90   12.799%   $156.6778   $156.68   $156.70   $156.70  
  Purchase #3 $35.34   12.274%   $39.6776   $39.68   $39.70   $39.70  
  Purchase #4 $140.68   7.706%   $151.5208   $151.52   $151.50   $151.50  
  Purchase #5 $218.43   6.513%   $232.6563   $232.66   $232.65   $232.70  
  Purchase #6 $217.43   3.621%   $225.3031   $225.30   $225.30   $225.30  
  Purchase #7 $100.97   7.634%   $108.678   $108.68   $108.70   $108.70  
  7 purchase totals = $908.30       $976.3657   $976.37   $976.40   $976.50