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 $59.84   9.800%   $65.7043   $65.70   $65.70   $65.70  
  Purchase #2 $217.81   13.247%   $246.6633   $246.66   $246.65   $246.70  
  Purchase #3 $240.27   10.397%   $265.2509   $265.25   $265.25   $265.30  
  Purchase #4 $194.81   3.488%   $201.605   $201.61   $201.60   $201.60  
  Purchase #5 $190.68   10.638%   $210.9645   $210.96   $210.95   $211.00  
  Purchase #6 $24.90   9.207%   $27.1925   $27.19   $27.20   $27.20  
  Purchase #7 $108.27   13.835%   $123.2492   $123.25   $123.25   $123.20  
  7 purchase totals = $1,036.58       $1,140.6297   $1,140.62   $1,140.60   $1,140.70