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 $250.39   10.364%   $276.3404   $276.34   $276.35   $276.30  
  Purchase #2 $150.99   9.864%   $165.8837   $165.88   $165.90   $165.90  
  Purchase #3 $225.85   12.111%   $253.2027   $253.20   $253.20   $253.20  
  Purchase #4 $18.85   13.464%   $21.388   $21.39   $21.40   $21.40  
  Purchase #5 $236.60   3.349%   $244.5237   $244.52   $244.50   $244.50  
  Purchase #6 $247.29   9.176%   $269.9813   $269.98   $270.00   $270.00  
  Purchase #7 $236.29   11.517%   $263.5035   $263.50   $263.50   $263.50  
  7 purchase totals = $1,366.26       $1,494.8233   $1,494.81   $1,494.85   $1,494.80