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 $181.92   3.345%   $188.0052   $188.01   $188.00   $188.00  
  Purchase #2 $94.90   11.730%   $106.0318   $106.03   $106.05   $106.00  
  Purchase #3 $54.33   8.553%   $58.9768   $58.98   $59.00   $59.00  
  Purchase #4 $21.59   13.580%   $24.5219   $24.52   $24.50   $24.50  
  Purchase #5 $224.91   10.361%   $248.2129   $248.21   $248.20   $248.20  
  Purchase #6 $192.67   4.719%   $201.7621   $201.76   $201.75   $201.80  
  Purchase #7 $205.48   3.288%   $212.2362   $212.24   $212.25   $212.20  
  7 purchase totals = $975.80       $1,039.7469   $1,039.75   $1,039.75   $1,039.70