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 $242.28   9.392%   $265.0349   $265.03   $265.05   $265.00  
  Purchase #2 $149.31   4.255%   $155.6631   $155.66   $155.65   $155.70  
  Purchase #3 $110.53   11.475%   $123.2133   $123.21   $123.20   $123.20  
  Purchase #4 $9.33   4.247%   $9.7262   $9.73   $9.75   $9.70  
  Purchase #5 $26.90   9.147%   $29.3605   $29.36   $29.35   $29.40  
  Purchase #6 $86.37   9.237%   $94.348   $94.35   $94.35   $94.30  
  Purchase #7 $186.32   6.547%   $198.5184   $198.52   $198.50   $198.50  
  7 purchase totals = $811.04       $875.8644   $875.86   $875.85   $875.80