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 $158.27   5.707%   $167.3025   $167.30   $167.30   $167.30  
  Purchase #2 $55.90   5.484%   $58.9656   $58.97   $58.95   $59.00  
  Purchase #3 $243.37   4.243%   $253.6962   $253.70   $253.70   $253.70  
  Purchase #4 $234.59   13.335%   $265.8726   $265.87   $265.85   $265.90  
  Purchase #5 $227.79   5.851%   $241.118   $241.12   $241.10   $241.10  
  Purchase #6 $190.35   10.167%   $209.7029   $209.70   $209.70   $209.70  
  Purchase #7 $63.45   10.547%   $70.1421   $70.14   $70.15   $70.10  
  7 purchase totals = $1,173.72       $1,266.7999   $1,266.80   $1,266.75   $1,266.80