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 $85.63   13.637%   $97.3074   $97.31   $97.30   $97.30  
  Purchase #2 $95.83   8.373%   $103.8538   $103.85   $103.85   $103.90  
  Purchase #3 $230.95   12.812%   $260.5393   $260.54   $260.55   $260.50  
  Purchase #4 $158.45   10.401%   $174.9304   $174.93   $174.95   $174.90  
  Purchase #5 $202.76   9.455%   $221.931   $221.93   $221.95   $221.90  
  Purchase #6 $161.58   12.518%   $181.8066   $181.81   $181.80   $181.80  
  Purchase #7 $12.61   7.727%   $13.5844   $13.58   $13.60   $13.60  
  7 purchase totals = $947.81       $1,053.9529   $1,053.95   $1,054.00   $1,053.90