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 $70.97   3.652%   $73.5618   $73.56   $73.55   $73.60  
  Purchase #2 $140.48   3.818%   $145.8435   $145.84   $145.85   $145.80  
  Purchase #3 $227.97   4.357%   $237.9027   $237.90   $237.90   $237.90  
  Purchase #4 $147.92   5.103%   $155.4684   $155.47   $155.45   $155.50  
  Purchase #5 $146.67   3.367%   $151.6084   $151.61   $151.60   $151.60  
  Purchase #6 $116.66   13.201%   $132.0603   $132.06   $132.05   $132.10  
  Purchase #7 $77.65   3.716%   $80.5355   $80.54   $80.55   $80.50  
  7 purchase totals = $928.32       $976.9806   $976.98   $976.95   $977.00