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 $136.85   9.277%   $149.5456   $149.55   $149.55   $149.50  
  Purchase #2 $126.26   9.730%   $138.5451   $138.55   $138.55   $138.50  
  Purchase #3 $73.59   9.214%   $80.3706   $80.37   $80.35   $80.40  
  Purchase #4 $227.73   3.504%   $235.7097   $235.71   $235.70   $235.70  
  Purchase #5 $65.75   11.328%   $73.1982   $73.20   $73.20   $73.20  
  Purchase #6 $156.30   4.805%   $163.8102   $163.81   $163.80   $163.80  
  Purchase #7 $197.71   10.212%   $217.9001   $217.90   $217.90   $217.90  
  7 purchase totals = $984.19       $1,059.0795   $1,059.09   $1,059.05   $1,059.00