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 $82.65   13.308%   $93.6491   $93.65   $93.65   $93.60  
  Purchase #2 $224.63   6.689%   $239.6555   $239.66   $239.65   $239.70  
  Purchase #3 $108.35   10.708%   $119.9521   $119.95   $119.95   $120.00  
  Purchase #4 $243.51   11.207%   $270.8002   $270.80   $270.80   $270.80  
  Purchase #5 $60.93   13.226%   $68.9886   $68.99   $69.00   $69.00  
  Purchase #6 $73.91   8.338%   $80.0726   $80.07   $80.05   $80.10  
  Purchase #7 $159.26   8.361%   $172.5757   $172.58   $172.60   $172.60  
  7 purchase totals = $953.24       $1,045.6938   $1,045.70   $1,045.70   $1,045.80