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 $220.71   5.273%   $232.348   $232.35   $232.35   $232.30  
  Purchase #2 $196.78   12.753%   $221.8754   $221.88   $221.90   $221.90  
  Purchase #3 $61.41   5.168%   $64.5837   $64.58   $64.60   $64.60  
  Purchase #4 $175.59   3.691%   $182.071   $182.07   $182.05   $182.10  
  Purchase #5 $48.32   13.674%   $54.9273   $54.93   $54.95   $54.90  
  Purchase #6 $238.66   12.844%   $269.3135   $269.31   $269.30   $269.30  
  Purchase #7 $31.87   7.765%   $34.3447   $34.34   $34.35   $34.30  
  7 purchase totals = $973.34       $1,059.4636   $1,059.46   $1,059.50   $1,059.40