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 $91.52   8.224%   $99.0466   $99.05   $99.05   $99.00  
  Purchase #2 $184.79   4.196%   $192.5438   $192.54   $192.55   $192.50  
  Purchase #3 $154.81   13.846%   $176.245   $176.25   $176.25   $176.20  
  Purchase #4 $83.38   11.253%   $92.7628   $92.76   $92.75   $92.80  
  Purchase #5 $41.26   12.200%   $46.2937   $46.29   $46.30   $46.30  
  Purchase #6 $224.68   11.645%   $250.844   $250.84   $250.85   $250.80  
  Purchase #7 $141.77   10.719%   $156.9663   $156.97   $156.95   $157.00  
  7 purchase totals = $922.21       $1,014.7022   $1,014.70   $1,014.70   $1,014.60