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 $165.68   13.764%   $188.4842   $188.48   $188.50   $188.50  
  Purchase #2 $201.76   3.504%   $208.8297   $208.83   $208.85   $208.80  
  Purchase #3 $184.66   7.593%   $198.6812   $198.68   $198.70   $198.70  
  Purchase #4 $88.33   4.754%   $92.5292   $92.53   $92.55   $92.50  
  Purchase #5 $224.75   8.415%   $243.6627   $243.66   $243.65   $243.70  
  Purchase #6 $53.60   8.617%   $58.2187   $58.22   $58.20   $58.20  
  Purchase #7 $39.27   9.398%   $42.9606   $42.96   $42.95   $43.00  
  7 purchase totals = $958.05       $1,033.3663   $1,033.36   $1,033.40   $1,033.40