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 $241.66   10.452%   $266.9183   $266.92   $266.90   $266.90  
  Purchase #2 $42.65   9.349%   $46.6373   $46.64   $46.65   $46.60  
  Purchase #3 $250.97   5.501%   $264.7759   $264.78   $264.80   $264.80  
  Purchase #4 $76.38   9.241%   $83.4383   $83.44   $83.45   $83.40  
  Purchase #5 $246.88   6.580%   $263.1247   $263.12   $263.10   $263.10  
  Purchase #6 $12.27   6.617%   $13.0819   $13.08   $13.10   $13.10  
  Purchase #7 $207.78   12.683%   $234.1327   $234.13   $234.15   $234.10  
  7 purchase totals = $1,078.59       $1,172.1091   $1,172.11   $1,172.15   $1,172.00