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 $121.62   3.712%   $126.1345   $126.13   $126.15   $126.10  
  Purchase #2 $244.89   7.135%   $262.3629   $262.36   $262.35   $262.40  
  Purchase #3 $44.94   6.699%   $47.9505   $47.95   $47.95   $48.00  
  Purchase #4 $165.50   4.861%   $173.545   $173.55   $173.55   $173.50  
  Purchase #5 $58.32   10.537%   $64.4652   $64.47   $64.45   $64.50  
  Purchase #6 $231.37   13.780%   $263.2528   $263.25   $263.25   $263.30  
  Purchase #7 $74.73   7.749%   $80.5208   $80.52   $80.50   $80.50  
  7 purchase totals = $941.37       $1,018.2317   $1,018.23   $1,018.20   $1,018.30