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 $221.69   11.743%   $247.7231   $247.72   $247.70   $247.70  
  Purchase #2 $141.70   6.732%   $151.2392   $151.24   $151.25   $151.20  
  Purchase #3 $160.31   11.599%   $178.9044   $178.90   $178.90   $178.90  
  Purchase #4 $41.91   12.860%   $47.2996   $47.30   $47.30   $47.30  
  Purchase #5 $239.52   13.836%   $272.66   $272.66   $272.65   $272.70  
  Purchase #6 $110.80   4.464%   $115.7461   $115.75   $115.75   $115.70  
  Purchase #7 $124.88   13.411%   $141.6277   $141.63   $141.65   $141.60  
  7 purchase totals = $1,040.81       $1,155.2001   $1,155.20   $1,155.20   $1,155.10