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 $214.91   12.436%   $241.6362   $241.64   $241.65   $241.60  
  Purchase #2 $123.26   9.711%   $135.2298   $135.23   $135.25   $135.20  
  Purchase #3 $54.93   3.528%   $56.8679   $56.87   $56.85   $56.90  
  Purchase #4 $205.78   8.288%   $222.835   $222.84   $222.85   $222.80  
  Purchase #5 $187.78   8.833%   $204.3666   $204.37   $204.35   $204.40  
  Purchase #6 $10.57   11.307%   $11.7651   $11.77   $11.75   $11.80  
  Purchase #7 $174.76   5.164%   $183.7846   $183.78   $183.80   $183.80  
  7 purchase totals = $971.99       $1,056.4852   $1,056.50   $1,056.50   $1,056.50