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 $246.27   3.764%   $255.5396   $255.54   $255.55   $255.50  
  Purchase #2 $215.75   4.214%   $224.8417   $224.84   $224.85   $224.80  
  Purchase #3 $97.90   7.786%   $105.5225   $105.52   $105.50   $105.50  
  Purchase #4 $208.67   8.281%   $225.95   $225.95   $225.95   $226.00  
  Purchase #5 $102.78   4.536%   $107.4421   $107.44   $107.45   $107.40  
  Purchase #6 $170.50   3.638%   $176.7028   $176.70   $176.70   $176.70  
  Purchase #7 $79.90   9.124%   $87.1901   $87.19   $87.20   $87.20  
  7 purchase totals = $1,121.77       $1,183.1888   $1,183.18   $1,183.20   $1,183.10