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 $70.52   3.523%   $73.0044   $73.00   $73.00   $73.00  
  Purchase #2 $94.45   8.622%   $102.5935   $102.59   $102.60   $102.60  
  Purchase #3 $244.78   5.654%   $258.6199   $258.62   $258.60   $258.60  
  Purchase #4 $59.74   5.688%   $63.138   $63.14   $63.15   $63.10  
  Purchase #5 $215.69   8.102%   $233.1652   $233.17   $233.15   $233.20  
  Purchase #6 $143.66   7.184%   $153.9805   $153.98   $154.00   $154.00  
  Purchase #7 $118.46   12.326%   $133.0614   $133.06   $133.05   $133.10  
  7 purchase totals = $947.30       $1,017.5629   $1,017.56   $1,017.55   $1,017.60