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 $46.62   6.840%   $49.8088   $49.81   $49.80   $49.80  
  Purchase #2 $175.29   8.359%   $189.9425   $189.94   $189.95   $189.90  
  Purchase #3 $187.65   6.611%   $200.0555   $200.06   $200.05   $200.10  
  Purchase #4 $88.68   8.293%   $96.0342   $96.03   $96.05   $96.00  
  Purchase #5 $59.58   7.390%   $63.983   $63.98   $64.00   $64.00  
  Purchase #6 $5.38   6.144%   $5.7105   $5.71   $5.70   $5.70  
  Purchase #7 $247.68   9.808%   $271.9725   $271.97   $271.95   $272.00  
  7 purchase totals = $810.88       $877.5070   $877.50   $877.50   $877.50