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 $192.39   6.717%   $205.3128   $205.31   $205.30   $205.30  
  Purchase #2 $15.62   6.609%   $16.6523   $16.65   $16.65   $16.70  
  Purchase #3 $90.70   13.608%   $103.0425   $103.04   $103.05   $103.00  
  Purchase #4 $174.35   12.356%   $195.8927   $195.89   $195.90   $195.90  
  Purchase #5 $6.82   9.590%   $7.474   $7.47   $7.45   $7.50  
  Purchase #6 $208.91   8.589%   $226.8533   $226.85   $226.85   $226.90  
  Purchase #7 $43.95   9.861%   $48.2839   $48.28   $48.30   $48.30  
  7 purchase totals = $732.74       $803.5115   $803.49   $803.50   $803.60