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 $182.38   6.839%   $194.853   $194.85   $194.85   $194.90  
  Purchase #2 $21.70   7.652%   $23.3605   $23.36   $23.35   $23.40  
  Purchase #3 $202.80   10.596%   $224.2887   $224.29   $224.30   $224.30  
  Purchase #4 $150.54   8.829%   $163.8312   $163.83   $163.85   $163.80  
  Purchase #5 $94.82   13.361%   $107.4889   $107.49   $107.50   $107.50  
  Purchase #6 $21.94   11.641%   $24.494   $24.49   $24.50   $24.50  
  Purchase #7 $160.95   12.309%   $180.7613   $180.76   $180.75   $180.80  
  7 purchase totals = $835.13       $919.0776   $919.07   $919.10   $919.20