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 $73.88   3.268%   $76.2944   $76.29   $76.30   $76.30  
  Purchase #2 $197.34   3.793%   $204.8251   $204.83   $204.85   $204.80  
  Purchase #3 $158.66   8.211%   $171.6876   $171.69   $171.70   $171.70  
  Purchase #4 $5.92   6.623%   $6.3121   $6.31   $6.30   $6.30  
  Purchase #5 $29.60   6.212%   $31.4388   $31.44   $31.45   $31.40  
  Purchase #6 $160.39   10.867%   $177.8196   $177.82   $177.80   $177.80  
  Purchase #7 $247.54   6.476%   $263.5707   $263.57   $263.55   $263.60  
  7 purchase totals = $873.33       $931.9483   $931.95   $931.95   $931.90