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 $196.27   5.275%   $206.6232   $206.62   $206.60   $206.60  
  Purchase #2 $83.31   13.769%   $94.781   $94.78   $94.80   $94.80  
  Purchase #3 $190.89   5.272%   $200.9537   $200.95   $200.95   $201.00  
  Purchase #4 $43.95   6.745%   $46.9144   $46.91   $46.90   $46.90  
  Purchase #5 $165.85   4.324%   $173.0214   $173.02   $173.00   $173.00  
  Purchase #6 $204.78   7.306%   $219.7412   $219.74   $219.75   $219.70  
  Purchase #7 $16.40   6.814%   $17.5175   $17.52   $17.50   $17.50  
  7 purchase totals = $901.45       $959.5524   $959.54   $959.50   $959.50