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 $126.95   11.704%   $141.8082   $141.81   $141.80   $141.80  
  Purchase #2 $241.74   13.346%   $274.0026   $274.00   $274.00   $274.00  
  Purchase #3 $155.81   8.692%   $169.353   $169.35   $169.35   $169.40  
  Purchase #4 $154.92   5.561%   $163.5351   $163.54   $163.55   $163.50  
  Purchase #5 $82.52   3.487%   $85.3975   $85.40   $85.40   $85.40  
  Purchase #6 $134.49   5.127%   $141.3853   $141.39   $141.40   $141.40  
  Purchase #7 $158.50   5.224%   $166.78   $166.78   $166.80   $166.80  
  7 purchase totals = $1,054.93       $1,142.2617   $1,142.27   $1,142.30   $1,142.30