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 $232.92   9.777%   $255.6926   $255.69   $255.70   $255.70  
  Purchase #2 $249.92   8.858%   $272.0579   $272.06   $272.05   $272.10  
  Purchase #3 $61.58   13.689%   $70.0097   $70.01   $70.00   $70.00  
  Purchase #4 $150.49   11.142%   $167.2576   $167.26   $167.25   $167.30  
  Purchase #5 $245.35   4.749%   $257.0017   $257.00   $257.00   $257.00  
  Purchase #6 $214.98   8.564%   $233.3909   $233.39   $233.40   $233.40  
  Purchase #7 $172.26   4.461%   $179.9445   $179.94   $179.95   $179.90  
  7 purchase totals = $1,327.50       $1,435.3549   $1,435.35   $1,435.35   $1,435.40