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 $58.39   5.476%   $61.5874   $61.59   $61.60   $61.60  
  Purchase #2 $145.29   9.340%   $158.8601   $158.86   $158.85   $158.90  
  Purchase #3 $207.73   13.633%   $236.0498   $236.05   $236.05   $236.00  
  Purchase #4 $142.28   9.654%   $156.0157   $156.02   $156.00   $156.00  
  Purchase #5 $119.74   6.232%   $127.2022   $127.20   $127.20   $127.20  
  Purchase #6 $22.57   5.279%   $23.7615   $23.76   $23.75   $23.80  
  Purchase #7 $11.62   6.197%   $12.3401   $12.34   $12.35   $12.30  
  7 purchase totals = $707.62       $775.8168   $775.82   $775.80   $775.80