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 $169.59   3.757%   $175.9615   $175.96   $175.95   $176.00  
  Purchase #2 $92.58   12.647%   $104.2886   $104.29   $104.30   $104.30  
  Purchase #3 $18.77   5.166%   $19.7397   $19.74   $19.75   $19.70  
  Purchase #4 $233.61   12.376%   $262.5216   $262.52   $262.50   $262.50  
  Purchase #5 $14.74   3.746%   $15.2922   $15.29   $15.30   $15.30  
  Purchase #6 $248.79   11.629%   $277.7218   $277.72   $277.70   $277.70  
  Purchase #7 $179.73   12.164%   $201.5924   $201.59   $201.60   $201.60  
  7 purchase totals = $957.81       $1,057.1178   $1,057.11   $1,057.10   $1,057.10