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 $152.66   8.605%   $165.7964   $165.80   $165.80   $165.80  
  Purchase #2 $203.64   10.264%   $224.5416   $224.54   $224.55   $224.50  
  Purchase #3 $244.40   13.743%   $277.9879   $277.99   $278.00   $278.00  
  Purchase #4 $153.39   6.373%   $163.1655   $163.17   $163.15   $163.20  
  Purchase #5 $123.69   8.681%   $134.4275   $134.43   $134.45   $134.40  
  Purchase #6 $161.85   6.677%   $172.6567   $172.66   $172.65   $172.70  
  Purchase #7 $24.38   4.408%   $25.4547   $25.45   $25.45   $25.50  
  7 purchase totals = $1,064.01       $1,164.0303   $1,164.04   $1,164.05   $1,164.10