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 $63.38   8.197%   $68.5753   $68.58   $68.60   $68.60  
  Purchase #2 $153.98   11.154%   $171.1549   $171.15   $171.15   $171.20  
  Purchase #3 $189.64   9.264%   $207.2082   $207.21   $207.20   $207.20  
  Purchase #4 $211.52   11.141%   $235.0854   $235.09   $235.10   $235.10  
  Purchase #5 $143.51   3.130%   $148.0019   $148.00   $148.00   $148.00  
  Purchase #6 $41.96   8.467%   $45.5128   $45.51   $45.50   $45.50  
  Purchase #7 $179.92   5.538%   $189.884   $189.88   $189.90   $189.90  
  7 purchase totals = $983.91       $1,065.4225   $1,065.42   $1,065.45   $1,065.50