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 $117.57   8.554%   $127.6269   $127.63   $127.65   $127.60  
  Purchase #2 $130.85   13.848%   $148.9701   $148.97   $148.95   $149.00  
  Purchase #3 $174.38   4.606%   $182.4119   $182.41   $182.40   $182.40  
  Purchase #4 $95.45   7.767%   $102.8636   $102.86   $102.85   $102.90  
  Purchase #5 $5.76   4.298%   $6.0076   $6.01   $6.00   $6.00  
  Purchase #6 $224.50   9.720%   $246.3214   $246.32   $246.30   $246.30  
  Purchase #7 $217.29   11.226%   $241.683   $241.68   $241.70   $241.70  
  7 purchase totals = $965.80       $1,055.8845   $1,055.88   $1,055.85   $1,055.90