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 $197.66   7.821%   $213.119   $213.12   $213.10   $213.10  
  Purchase #2 $234.52   8.716%   $254.9608   $254.96   $254.95   $255.00  
  Purchase #3 $79.76   11.562%   $88.9819   $88.98   $89.00   $89.00  
  Purchase #4 $114.76   11.665%   $128.1468   $128.15   $128.15   $128.10  
  Purchase #5 $50.38   6.589%   $53.6995   $53.70   $53.70   $53.70  
  Purchase #6 $129.80   9.581%   $142.2361   $142.24   $142.25   $142.20  
  Purchase #7 $116.64   10.405%   $128.7764   $128.78   $128.80   $128.80  
  7 purchase totals = $923.52       $1,009.9205   $1,009.93   $1,009.95   $1,009.90