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 $40.35   7.562%   $43.4013   $43.40   $43.40   $43.40  
  Purchase #2 $209.54   6.838%   $223.8683   $223.87   $223.85   $223.90  
  Purchase #3 $173.30   8.438%   $187.9231   $187.92   $187.90   $187.90  
  Purchase #4 $153.72   5.209%   $161.7273   $161.73   $161.75   $161.70  
  Purchase #5 $8.94   8.415%   $9.6923   $9.69   $9.70   $9.70  
  Purchase #6 $211.31   9.547%   $231.4838   $231.48   $231.50   $231.50  
  Purchase #7 $139.52   12.248%   $156.6084   $156.61   $156.60   $156.60  
  7 purchase totals = $936.68       $1,014.7045   $1,014.70   $1,014.70   $1,014.70