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 $62.47   11.591%   $69.7109   $69.71   $69.70   $69.70  
  Purchase #2 $126.25   11.320%   $140.5415   $140.54   $140.55   $140.50  
  Purchase #3 $23.27   3.644%   $24.118   $24.12   $24.10   $24.10  
  Purchase #4 $165.33   7.119%   $177.0998   $177.10   $177.10   $177.10  
  Purchase #5 $225.96   4.417%   $235.9407   $235.94   $235.95   $235.90  
  Purchase #6 $130.89   10.224%   $144.2722   $144.27   $144.25   $144.30  
  Purchase #7 $113.56   10.644%   $125.6473   $125.65   $125.65   $125.60  
  7 purchase totals = $847.73       $917.3304   $917.33   $917.30   $917.20