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 $131.28   3.328%   $135.649   $135.65   $135.65   $135.60  
  Purchase #2 $96.35   4.695%   $100.8736   $100.87   $100.85   $100.90  
  Purchase #3 $110.68   7.643%   $119.1393   $119.14   $119.15   $119.10  
  Purchase #4 $215.79   13.802%   $245.5733   $245.57   $245.55   $245.60  
  Purchase #5 $205.26   11.291%   $228.4359   $228.44   $228.45   $228.40  
  Purchase #6 $244.91   5.444%   $258.2429   $258.24   $258.25   $258.20  
  Purchase #7 $118.56   10.639%   $131.1736   $131.17   $131.15   $131.20  
  7 purchase totals = $1,122.83       $1,219.0876   $1,219.08   $1,219.05   $1,219.00