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 $177.73   13.539%   $201.7929   $201.79   $201.80   $201.80  
  Purchase #2 $176.71   9.510%   $193.5151   $193.52   $193.50   $193.50  
  Purchase #3 $227.37   10.354%   $250.9119   $250.91   $250.90   $250.90  
  Purchase #4 $169.27   4.317%   $176.5774   $176.58   $176.60   $176.60  
  Purchase #5 $163.62   6.342%   $173.9968   $174.00   $174.00   $174.00  
  Purchase #6 $60.67   3.850%   $63.0058   $63.01   $63.00   $63.00  
  Purchase #7 $32.39   11.439%   $36.0951   $36.10   $36.10   $36.10  
  7 purchase totals = $1,007.76       $1,095.8950   $1,095.91   $1,095.90   $1,095.90