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 $225.28   3.415%   $232.9733   $232.97   $232.95   $233.00  
  Purchase #2 $95.45   6.219%   $101.386   $101.39   $101.40   $101.40  
  Purchase #3 $77.53   11.217%   $86.2265   $86.23   $86.25   $86.20  
  Purchase #4 $53.90   11.820%   $60.271   $60.27   $60.25   $60.30  
  Purchase #5 $154.96   10.737%   $171.5981   $171.60   $171.60   $171.60  
  Purchase #6 $130.69   5.199%   $137.4846   $137.48   $137.50   $137.50  
  Purchase #7 $232.27   9.373%   $254.0407   $254.04   $254.05   $254.00  
  7 purchase totals = $970.08       $1,043.9802   $1,043.98   $1,044.00   $1,044.00