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 $243.40   5.567%   $256.9501   $256.95   $256.95   $257.00  
  Purchase #2 $213.70   9.206%   $233.3732   $233.37   $233.35   $233.40  
  Purchase #3 $61.50   9.206%   $67.1617   $67.16   $67.15   $67.20  
  Purchase #4 $75.35   5.434%   $79.4445   $79.44   $79.45   $79.40  
  Purchase #5 $184.79   10.643%   $204.4572   $204.46   $204.45   $204.50  
  Purchase #6 $49.33   4.413%   $51.5069   $51.51   $51.50   $51.50  
  Purchase #7 $200.36   7.656%   $215.6996   $215.70   $215.70   $215.70  
  7 purchase totals = $1,028.43       $1,108.5932   $1,108.59   $1,108.55   $1,108.70