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 $88.32   10.240%   $97.364   $97.36   $97.35   $97.40  
  Purchase #2 $49.56   7.441%   $53.2478   $53.25   $53.25   $53.20  
  Purchase #3 $187.53   5.373%   $197.606   $197.61   $197.60   $197.60  
  Purchase #4 $235.62   6.778%   $251.5903   $251.59   $251.60   $251.60  
  Purchase #5 $79.77   11.486%   $88.9324   $88.93   $88.95   $88.90  
  Purchase #6 $231.49   9.270%   $252.9491   $252.95   $252.95   $252.90  
  Purchase #7 $132.68   6.470%   $141.2644   $141.26   $141.25   $141.30  
  7 purchase totals = $1,004.97       $1,082.9540   $1,082.95   $1,082.95   $1,082.90