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 $64.27   12.174%   $72.0942   $72.09   $72.10   $72.10  
  Purchase #2 $207.59   9.425%   $227.1554   $227.16   $227.15   $227.20  
  Purchase #3 $84.94   12.445%   $95.5108   $95.51   $95.50   $95.50  
  Purchase #4 $243.47   10.291%   $268.5255   $268.53   $268.55   $268.50  
  Purchase #5 $134.76   8.819%   $146.6445   $146.64   $146.65   $146.60  
  Purchase #6 $192.32   10.755%   $213.004   $213.00   $213.00   $213.00  
  Purchase #7 $156.30   8.383%   $169.4026   $169.40   $169.40   $169.40  
  7 purchase totals = $1,083.65       $1,192.3370   $1,192.33   $1,192.35   $1,192.30