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 $84.64   8.522%   $91.853   $91.85   $91.85   $91.90  
  Purchase #2 $95.63   11.846%   $106.9583   $106.96   $106.95   $107.00  
  Purchase #3 $26.98   5.429%   $28.4447   $28.44   $28.45   $28.40  
  Purchase #4 $217.58   3.786%   $225.8176   $225.82   $225.80   $225.80  
  Purchase #5 $69.73   12.343%   $78.3368   $78.34   $78.35   $78.30  
  Purchase #6 $197.48   11.106%   $219.4121   $219.41   $219.40   $219.40  
  Purchase #7 $239.62   11.405%   $266.9487   $266.95   $266.95   $266.90  
  7 purchase totals = $931.66       $1,017.7712   $1,017.77   $1,017.75   $1,017.70