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 $241.39   12.143%   $270.702   $270.70   $270.70   $270.70  
  Purchase #2 $62.29   9.150%   $67.9895   $67.99   $68.00   $68.00  
  Purchase #3 $116.35   6.139%   $123.4927   $123.49   $123.50   $123.50  
  Purchase #4 $92.81   13.708%   $105.5324   $105.53   $105.55   $105.50  
  Purchase #5 $39.62   5.785%   $41.912   $41.91   $41.90   $41.90  
  Purchase #6 $188.48   10.791%   $208.8189   $208.82   $208.80   $208.80  
  Purchase #7 $246.44   13.130%   $278.7976   $278.80   $278.80   $278.80  
  7 purchase totals = $987.38       $1,097.2451   $1,097.24   $1,097.25   $1,097.20