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 $209.82   8.177%   $226.977   $226.98   $227.00   $227.00  
  Purchase #2 $73.25   5.427%   $77.2253   $77.23   $77.25   $77.20  
  Purchase #3 $19.82   5.758%   $20.9612   $20.96   $20.95   $21.00  
  Purchase #4 $133.78   7.770%   $144.1747   $144.17   $144.15   $144.20  
  Purchase #5 $96.85   10.304%   $106.8294   $106.83   $106.85   $106.80  
  Purchase #6 $165.40   9.439%   $181.0121   $181.01   $181.00   $181.00  
  Purchase #7 $222.57   6.456%   $236.9391   $236.94   $236.95   $236.90  
  7 purchase totals = $921.49       $994.1188   $994.12   $994.15   $994.10