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 $50.71   10.796%   $56.1847   $56.18   $56.20   $56.20  
  Purchase #2 $110.63   13.252%   $125.2907   $125.29   $125.30   $125.30  
  Purchase #3 $172.60   6.651%   $184.0796   $184.08   $184.10   $184.10  
  Purchase #4 $169.64   8.266%   $183.6624   $183.66   $183.65   $183.70  
  Purchase #5 $148.60   4.676%   $155.5485   $155.55   $155.55   $155.50  
  Purchase #6 $239.42   12.264%   $268.7825   $268.78   $268.80   $268.80  
  Purchase #7 $38.61   5.237%   $40.632   $40.63   $40.65   $40.60  
  7 purchase totals = $930.21       $1,014.1804   $1,014.17   $1,014.25   $1,014.20