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 $85.69   8.673%   $93.1219   $93.12   $93.10   $93.10  
  Purchase #2 $204.99   13.739%   $233.1536   $233.15   $233.15   $233.20  
  Purchase #3 $47.47   12.277%   $53.2979   $53.30   $53.30   $53.30  
  Purchase #4 $214.46   8.283%   $232.2237   $232.22   $232.20   $232.20  
  Purchase #5 $179.51   4.866%   $188.245   $188.25   $188.25   $188.20  
  Purchase #6 $149.90   11.599%   $167.2869   $167.29   $167.30   $167.30  
  Purchase #7 $217.81   5.683%   $230.1881   $230.19   $230.20   $230.20  
  7 purchase totals = $1,099.83       $1,197.5171   $1,197.52   $1,197.50   $1,197.50