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 $215.93   7.406%   $231.9218   $231.92   $231.90   $231.90  
  Purchase #2 $62.76   8.286%   $67.9603   $67.96   $67.95   $68.00  
  Purchase #3 $123.46   8.148%   $133.5195   $133.52   $133.50   $133.50  
  Purchase #4 $206.76   3.467%   $213.9284   $213.93   $213.95   $213.90  
  Purchase #5 $246.87   12.587%   $277.9435   $277.94   $277.95   $277.90  
  Purchase #6 $193.32   4.625%   $202.2611   $202.26   $202.25   $202.30  
  Purchase #7 $108.46   6.680%   $115.7051   $115.71   $115.70   $115.70  
  7 purchase totals = $1,157.56       $1,243.2397   $1,243.24   $1,243.20   $1,243.20