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 $59.59   3.661%   $61.7716   $61.77   $61.75   $61.80  
  Purchase #2 $99.91   4.836%   $104.7416   $104.74   $104.75   $104.70  
  Purchase #3 $169.90   5.588%   $179.394   $179.39   $179.40   $179.40  
  Purchase #4 $28.68   5.109%   $30.1453   $30.15   $30.15   $30.10  
  Purchase #5 $181.84   11.662%   $203.0462   $203.05   $203.05   $203.00  
  Purchase #6 $5.53   3.537%   $5.7256   $5.73   $5.75   $5.70  
  Purchase #7 $17.73   7.160%   $18.9995   $19.00   $19.00   $19.00  
  7 purchase totals = $563.18       $603.8238   $603.83   $603.85   $603.70