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 $32.99   5.614%   $34.8421   $34.84   $34.85   $34.80  
  Purchase #2 $53.48   11.693%   $59.7334   $59.73   $59.75   $59.70  
  Purchase #3 $71.73   7.366%   $77.0136   $77.01   $77.00   $77.00  
  Purchase #4 $58.34   3.349%   $60.2938   $60.29   $60.30   $60.30  
  Purchase #5 $133.53   5.874%   $141.3736   $141.37   $141.35   $141.40  
  Purchase #6 $165.48   9.847%   $181.7748   $181.77   $181.75   $181.80  
  Purchase #7 $65.31   8.563%   $70.9025   $70.90   $70.90   $70.90  
  7 purchase totals = $580.86       $625.9338   $625.91   $625.90   $625.90