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 $38.47   13.198%   $43.5473   $43.55   $43.55   $43.50  
  Purchase #2 $191.74   10.159%   $211.2189   $211.22   $211.20   $211.20  
  Purchase #3 $241.67   11.410%   $269.2445   $269.24   $269.25   $269.20  
  Purchase #4 $24.80   9.702%   $27.2061   $27.21   $27.20   $27.20  
  Purchase #5 $175.81   13.405%   $199.3773   $199.38   $199.40   $199.40  
  Purchase #6 $220.64   3.129%   $227.5438   $227.54   $227.55   $227.50  
  Purchase #7 $161.85   12.399%   $181.9178   $181.92   $181.90   $181.90  
  7 purchase totals = $1,054.98       $1,160.0557   $1,160.06   $1,160.05   $1,159.90