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 $206.84   13.203%   $234.1491   $234.15   $234.15   $234.10  
  Purchase #2 $170.53   6.244%   $181.1779   $181.18   $181.20   $181.20  
  Purchase #3 $220.56   4.869%   $231.2991   $231.30   $231.30   $231.30  
  Purchase #4 $65.62   8.378%   $71.1176   $71.12   $71.10   $71.10  
  Purchase #5 $63.27   5.847%   $66.9694   $66.97   $66.95   $67.00  
  Purchase #6 $143.76   5.652%   $151.8853   $151.89   $151.90   $151.90  
  Purchase #7 $81.99   6.459%   $87.2857   $87.29   $87.30   $87.30  
  7 purchase totals = $952.57       $1,023.8841   $1,023.90   $1,023.90   $1,023.90