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 $230.74   12.767%   $260.1986   $260.20   $260.20   $260.20  
  Purchase #2 $155.30   6.262%   $165.0249   $165.02   $165.00   $165.00  
  Purchase #3 $108.80   9.716%   $119.371   $119.37   $119.35   $119.40  
  Purchase #4 $239.62   5.865%   $253.6737   $253.67   $253.65   $253.70  
  Purchase #5 $232.52   8.242%   $251.6843   $251.68   $251.70   $251.70  
  Purchase #6 $55.53   9.178%   $60.6265   $60.63   $60.65   $60.60  
  Purchase #7 $169.42   9.171%   $184.9575   $184.96   $184.95   $185.00  
  7 purchase totals = $1,191.93       $1,295.5365   $1,295.53   $1,295.50   $1,295.60