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 $217.91   10.600%   $241.0085   $241.01   $241.00   $241.00  
  Purchase #2 $150.77   6.550%   $160.6454   $160.65   $160.65   $160.60  
  Purchase #3 $135.99   8.817%   $147.9802   $147.98   $148.00   $148.00  
  Purchase #4 $46.65   12.515%   $52.4882   $52.49   $52.50   $52.50  
  Purchase #5 $175.37   6.321%   $186.4551   $186.46   $186.45   $186.50  
  Purchase #6 $173.94   6.823%   $185.8079   $185.81   $185.80   $185.80  
  Purchase #7 $146.98   13.140%   $166.2932   $166.29   $166.30   $166.30  
  7 purchase totals = $1,047.61       $1,140.6785   $1,140.69   $1,140.70   $1,140.70