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 $241.79   11.632%   $269.915   $269.92   $269.90   $269.90  
  Purchase #2 $198.38   12.445%   $223.0684   $223.07   $223.05   $223.10  
  Purchase #3 $57.71   12.797%   $65.0951   $65.10   $65.10   $65.10  
  Purchase #4 $26.86   11.831%   $30.0378   $30.04   $30.05   $30.00  
  Purchase #5 $156.87   3.571%   $162.4718   $162.47   $162.45   $162.50  
  Purchase #6 $69.55   3.317%   $71.857   $71.86   $71.85   $71.90  
  Purchase #7 $62.44   10.434%   $68.955   $68.96   $68.95   $69.00  
  7 purchase totals = $813.60       $891.4001   $891.42   $891.35   $891.50