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 $146.60   3.443%   $151.6474   $151.65   $151.65   $151.60  
  Purchase #2 $115.58   7.867%   $124.6727   $124.67   $124.65   $124.70  
  Purchase #3 $6.38   8.383%   $6.9148   $6.91   $6.90   $6.90  
  Purchase #4 $172.87   4.196%   $180.1236   $180.12   $180.10   $180.10  
  Purchase #5 $53.48   5.868%   $56.6182   $56.62   $56.60   $56.60  
  Purchase #6 $193.29   5.304%   $203.5421   $203.54   $203.55   $203.50  
  Purchase #7 $210.92   3.280%   $217.8382   $217.84   $217.85   $217.80  
  7 purchase totals = $899.12       $941.3570   $941.35   $941.30   $941.20