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 $241.77   7.824%   $260.6861   $260.69   $260.70   $260.70  
  Purchase #2 $71.41   11.397%   $79.5486   $79.55   $79.55   $79.50  
  Purchase #3 $204.60   9.566%   $224.172   $224.17   $224.15   $224.20  
  Purchase #4 $192.70   5.550%   $203.3949   $203.39   $203.40   $203.40  
  Purchase #5 $105.52   6.549%   $112.4305   $112.43   $112.45   $112.40  
  Purchase #6 $76.56   4.654%   $80.1231   $80.12   $80.10   $80.10  
  Purchase #7 $65.60   12.205%   $73.6065   $73.61   $73.60   $73.60  
  7 purchase totals = $958.16       $1,033.9617   $1,033.96   $1,033.95   $1,033.90