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 $162.76   13.313%   $184.4282   $184.43   $184.45   $184.40  
  Purchase #2 $247.84   4.626%   $259.3051   $259.31   $259.30   $259.30  
  Purchase #3 $69.56   3.532%   $72.0169   $72.02   $72.00   $72.00  
  Purchase #4 $109.33   7.263%   $117.2706   $117.27   $117.25   $117.30  
  Purchase #5 $121.28   8.299%   $131.345   $131.35   $131.35   $131.30  
  Purchase #6 $36.70   13.342%   $41.5965   $41.60   $41.60   $41.60  
  Purchase #7 $239.55   5.206%   $252.021   $252.02   $252.00   $252.00  
  7 purchase totals = $987.02       $1,057.9833   $1,058.00   $1,057.95   $1,057.90