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 $165.41   7.647%   $178.0589   $178.06   $178.05   $178.10  
  Purchase #2 $128.74   10.263%   $141.9526   $141.95   $141.95   $142.00  
  Purchase #3 $228.76   4.455%   $238.9513   $238.95   $238.95   $239.00  
  Purchase #4 $76.74   11.481%   $85.5505   $85.55   $85.55   $85.60  
  Purchase #5 $216.94   13.690%   $246.6391   $246.64   $246.65   $246.60  
  Purchase #6 $165.61   6.860%   $176.9708   $176.97   $176.95   $177.00  
  Purchase #7 $23.57   6.634%   $25.1336   $25.13   $25.15   $25.10  
  7 purchase totals = $1,005.77       $1,093.2568   $1,093.25   $1,093.25   $1,093.40