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 $73.61   6.722%   $78.5581   $78.56   $78.55   $78.60  
  Purchase #2 $139.89   7.117%   $149.846   $149.85   $149.85   $149.80  
  Purchase #3 $133.38   6.582%   $142.1591   $142.16   $142.15   $142.20  
  Purchase #4 $77.28   12.124%   $86.6494   $86.65   $86.65   $86.60  
  Purchase #5 $61.29   9.473%   $67.096   $67.10   $67.10   $67.10  
  Purchase #6 $185.89   8.596%   $201.8691   $201.87   $201.85   $201.90  
  Purchase #7 $203.72   11.271%   $226.6813   $226.68   $226.70   $226.70  
  7 purchase totals = $875.06       $952.8590   $952.87   $952.85   $952.90