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 $95.66   12.416%   $107.5371   $107.54   $107.55   $107.50  
  Purchase #2 $6.42   4.155%   $6.6868   $6.69   $6.70   $6.70  
  Purchase #3 $59.34   6.208%   $63.0238   $63.02   $63.00   $63.00  
  Purchase #4 $158.80   9.668%   $174.1528   $174.15   $174.15   $174.20  
  Purchase #5 $169.55   11.615%   $189.2432   $189.24   $189.25   $189.20  
  Purchase #6 $231.27   13.751%   $263.0719   $263.07   $263.05   $263.10  
  Purchase #7 $54.32   7.113%   $58.1838   $58.18   $58.20   $58.20  
  7 purchase totals = $775.36       $861.8994   $861.89   $861.90   $861.90