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 $214.44   11.259%   $238.5838   $238.58   $238.60   $238.60  
  Purchase #2 $123.48   10.278%   $136.1713   $136.17   $136.15   $136.20  
  Purchase #3 $139.95   8.823%   $152.2978   $152.30   $152.30   $152.30  
  Purchase #4 $55.85   7.532%   $60.0566   $60.06   $60.05   $60.10  
  Purchase #5 $75.82   13.250%   $85.8662   $85.87   $85.85   $85.90  
  Purchase #6 $156.95   5.355%   $165.3547   $165.35   $165.35   $165.40  
  Purchase #7 $219.47   5.343%   $231.1963   $231.20   $231.20   $231.20  
  7 purchase totals = $985.96       $1,069.5267   $1,069.53   $1,069.50   $1,069.70