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 $93.88   13.691%   $106.7331   $106.73   $106.75   $106.70  
  Purchase #2 $185.68   4.192%   $193.4637   $193.46   $193.45   $193.50  
  Purchase #3 $44.63   11.453%   $49.7415   $49.74   $49.75   $49.70  
  Purchase #4 $215.31   4.671%   $225.3671   $225.37   $225.35   $225.40  
  Purchase #5 $187.41   8.563%   $203.4579   $203.46   $203.45   $203.50  
  Purchase #6 $102.52   13.454%   $116.313   $116.31   $116.30   $116.30  
  Purchase #7 $121.97   3.429%   $126.1524   $126.15   $126.15   $126.20  
  7 purchase totals = $951.40       $1,021.2287   $1,021.22   $1,021.20   $1,021.30