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 $130.52   10.174%   $143.7991   $143.80   $143.80   $143.80  
  Purchase #2 $60.42   13.652%   $68.6685   $68.67   $68.65   $68.70  
  Purchase #3 $88.93   3.407%   $91.9598   $91.96   $91.95   $92.00  
  Purchase #4 $108.95   6.429%   $115.9544   $115.95   $115.95   $116.00  
  Purchase #5 $250.34   8.136%   $270.7077   $270.71   $270.70   $270.70  
  Purchase #6 $89.74   6.418%   $95.4995   $95.50   $95.50   $95.50  
  Purchase #7 $216.47   8.845%   $235.6168   $235.62   $235.60   $235.60  
  7 purchase totals = $945.37       $1,022.2058   $1,022.21   $1,022.15   $1,022.30