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 $58.83   10.576%   $65.0519   $65.05   $65.05   $65.10  
  Purchase #2 $138.86   10.371%   $153.2612   $153.26   $153.25   $153.30  
  Purchase #3 $221.48   8.257%   $239.7676   $239.77   $239.75   $239.80  
  Purchase #4 $100.97   3.444%   $104.4474   $104.45   $104.45   $104.40  
  Purchase #5 $223.92   9.667%   $245.5663   $245.57   $245.55   $245.60  
  Purchase #6 $111.49   11.387%   $124.1854   $124.19   $124.20   $124.20  
  Purchase #7 $224.37   9.309%   $245.2566   $245.26   $245.25   $245.30  
  7 purchase totals = $1,079.92       $1,177.5364   $1,177.55   $1,177.50   $1,177.70