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 $241.53   11.698%   $269.7842   $269.78   $269.80   $269.80  
  Purchase #2 $52.85   12.775%   $59.6016   $59.60   $59.60   $59.60  
  Purchase #3 $217.37   5.327%   $228.9493   $228.95   $228.95   $228.90  
  Purchase #4 $239.43   5.312%   $252.1485   $252.15   $252.15   $252.10  
  Purchase #5 $223.64   3.764%   $232.0578   $232.06   $232.05   $232.10  
  Purchase #6 $174.67   3.104%   $180.0918   $180.09   $180.10   $180.10  
  Purchase #7 $65.52   12.829%   $73.9256   $73.93   $73.95   $73.90  
  7 purchase totals = $1,215.01       $1,296.5588   $1,296.56   $1,296.60   $1,296.50