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 $160.78   3.212%   $165.9443   $165.94   $165.95   $165.90  
  Purchase #2 $238.46   12.542%   $268.3677   $268.37   $268.35   $268.40  
  Purchase #3 $152.99   12.783%   $172.5467   $172.55   $172.55   $172.50  
  Purchase #4 $53.35   10.566%   $58.987   $58.99   $59.00   $59.00  
  Purchase #5 $89.97   12.361%   $101.0912   $101.09   $101.10   $101.10  
  Purchase #6 $214.64   6.752%   $229.1325   $229.13   $229.15   $229.10  
  Purchase #7 $199.88   11.732%   $223.3299   $223.33   $223.35   $223.30  
  7 purchase totals = $1,110.07       $1,219.3993   $1,219.40   $1,219.45   $1,219.30