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 $97.64   5.494%   $103.0043   $103.00   $103.00   $103.00  
  Purchase #2 $160.98   9.306%   $175.9608   $175.96   $175.95   $176.00  
  Purchase #3 $138.94   11.618%   $155.082   $155.08   $155.10   $155.10  
  Purchase #4 $27.89   10.239%   $30.7457   $30.75   $30.75   $30.70  
  Purchase #5 $124.56   10.494%   $137.6313   $137.63   $137.65   $137.60  
  Purchase #6 $31.33   3.670%   $32.4798   $32.48   $32.50   $32.50  
  Purchase #7 $229.68   7.357%   $246.5776   $246.58   $246.60   $246.60  
  7 purchase totals = $811.02       $881.4815   $881.48   $881.55   $881.50