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 $129.82   10.643%   $143.6367   $143.64   $143.65   $143.60  
  Purchase #2 $65.28   3.695%   $67.6921   $67.69   $67.70   $67.70  
  Purchase #3 $5.87   6.703%   $6.2635   $6.26   $6.25   $6.30  
  Purchase #4 $118.36   7.366%   $127.0784   $127.08   $127.10   $127.10  
  Purchase #5 $56.78   3.850%   $58.966   $58.97   $58.95   $59.00  
  Purchase #6 $84.39   11.739%   $94.2965   $94.30   $94.30   $94.30  
  Purchase #7 $213.89   10.642%   $236.6522   $236.65   $236.65   $236.70  
  7 purchase totals = $674.39       $734.5854   $734.59   $734.60   $734.70