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 $245.42   10.297%   $270.6909   $270.69   $270.70   $270.70  
  Purchase #2 $144.79   8.368%   $156.906   $156.91   $156.90   $156.90  
  Purchase #3 $95.99   10.461%   $106.0315   $106.03   $106.05   $106.00  
  Purchase #4 $118.52   10.759%   $131.2716   $131.27   $131.25   $131.30  
  Purchase #5 $146.85   6.475%   $156.3585   $156.36   $156.35   $156.40  
  Purchase #6 $201.29   12.563%   $226.5781   $226.58   $226.60   $226.60  
  Purchase #7 $115.85   5.344%   $122.041   $122.04   $122.05   $122.00  
  7 purchase totals = $1,068.71       $1,169.8776   $1,169.88   $1,169.90   $1,169.90