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 $205.56   13.843%   $234.0157   $234.02   $234.00   $234.00  
  Purchase #2 $171.65   4.317%   $179.0601   $179.06   $179.05   $179.10  
  Purchase #3 $185.50   4.126%   $193.1537   $193.15   $193.15   $193.20  
  Purchase #4 $244.72   7.355%   $262.7192   $262.72   $262.70   $262.70  
  Purchase #5 $81.26   13.373%   $92.1269   $92.13   $92.15   $92.10  
  Purchase #6 $156.90   8.757%   $170.6397   $170.64   $170.65   $170.60  
  Purchase #7 $159.92   10.352%   $176.4749   $176.47   $176.45   $176.50  
  7 purchase totals = $1,205.51       $1,308.1902   $1,308.19   $1,308.15   $1,308.20