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 $119.68   6.236%   $127.1432   $127.14   $127.15   $127.10  
  Purchase #2 $162.26   10.637%   $179.5196   $179.52   $179.50   $179.50  
  Purchase #3 $180.26   12.861%   $203.4432   $203.44   $203.45   $203.40  
  Purchase #4 $231.38   4.820%   $242.5325   $242.53   $242.55   $242.50  
  Purchase #5 $8.57   11.408%   $9.5477   $9.55   $9.55   $9.50  
  Purchase #6 $157.95   9.768%   $173.3786   $173.38   $173.40   $173.40  
  Purchase #7 $155.92   13.557%   $177.0581   $177.06   $177.05   $177.10  
  7 purchase totals = $1,016.02       $1,112.6229   $1,112.62   $1,112.65   $1,112.50