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 $116.26   11.823%   $130.0054   $130.01   $130.00   $130.00  
  Purchase #2 $102.31   3.832%   $106.2305   $106.23   $106.25   $106.20  
  Purchase #3 $138.92   7.325%   $149.0959   $149.10   $149.10   $149.10  
  Purchase #4 $211.97   10.531%   $234.2926   $234.29   $234.30   $234.30  
  Purchase #5 $66.75   8.578%   $72.4758   $72.48   $72.50   $72.50  
  Purchase #6 $215.54   5.182%   $226.7093   $226.71   $226.70   $226.70  
  Purchase #7 $59.99   8.627%   $65.1653   $65.17   $65.15   $65.20  
  7 purchase totals = $911.74       $983.9748   $983.99   $984.00   $984.00