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 $59.30   9.445%   $64.9009   $64.90   $64.90   $64.90  
  Purchase #2 $125.25   8.546%   $135.9539   $135.95   $135.95   $136.00  
  Purchase #3 $153.78   7.868%   $165.8794   $165.88   $165.90   $165.90  
  Purchase #4 $232.28   13.438%   $263.4938   $263.49   $263.50   $263.50  
  Purchase #5 $24.80   3.556%   $25.6819   $25.68   $25.70   $25.70  
  Purchase #6 $192.69   5.444%   $203.18   $203.18   $203.20   $203.20  
  Purchase #7 $236.83   6.595%   $252.4489   $252.45   $252.45   $252.40  
  7 purchase totals = $1,024.93       $1,111.5388   $1,111.53   $1,111.60   $1,111.60