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 $92.76   9.709%   $101.7661   $101.77   $101.75   $101.80  
  Purchase #2 $159.88   12.182%   $179.3566   $179.36   $179.35   $179.40  
  Purchase #3 $221.96   7.858%   $239.4016   $239.40   $239.40   $239.40  
  Purchase #4 $45.55   8.304%   $49.3325   $49.33   $49.35   $49.30  
  Purchase #5 $150.65   8.249%   $163.0771   $163.08   $163.10   $163.10  
  Purchase #6 $78.39   7.641%   $84.3798   $84.38   $84.40   $84.40  
  Purchase #7 $184.91   11.658%   $206.4668   $206.47   $206.45   $206.50  
  7 purchase totals = $934.10       $1,023.7805   $1,023.79   $1,023.80   $1,023.90