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 $167.37   9.344%   $183.0091   $183.01   $183.00   $183.00  
  Purchase #2 $169.51   3.659%   $175.7124   $175.71   $175.70   $175.70  
  Purchase #3 $24.94   3.241%   $25.7483   $25.75   $25.75   $25.70  
  Purchase #4 $88.54   4.602%   $92.6146   $92.61   $92.60   $92.60  
  Purchase #5 $102.66   3.520%   $106.2736   $106.27   $106.25   $106.30  
  Purchase #6 $221.53   5.457%   $233.6189   $233.62   $233.60   $233.60  
  Purchase #7 $224.81   8.276%   $243.4153   $243.42   $243.40   $243.40  
  7 purchase totals = $999.36       $1,060.3922   $1,060.39   $1,060.30   $1,060.30