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 $54.77   12.836%   $61.8003   $61.80   $61.80   $61.80  
  Purchase #2 $241.37   11.505%   $269.1396   $269.14   $269.15   $269.10  
  Purchase #3 $180.57   10.492%   $199.5154   $199.52   $199.50   $199.50  
  Purchase #4 $46.83   10.424%   $51.7116   $51.71   $51.70   $51.70  
  Purchase #5 $241.62   3.560%   $250.2217   $250.22   $250.20   $250.20  
  Purchase #6 $83.97   9.176%   $91.6751   $91.68   $91.70   $91.70  
  Purchase #7 $231.91   11.306%   $258.1297   $258.13   $258.15   $258.10  
  7 purchase totals = $1,081.04       $1,182.1934   $1,182.20   $1,182.20   $1,182.10