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 $66.64   3.172%   $68.7538   $68.75   $68.75   $68.80  
  Purchase #2 $10.54   6.146%   $11.1878   $11.19   $11.20   $11.20  
  Purchase #3 $241.43   9.365%   $264.0399   $264.04   $264.05   $264.00  
  Purchase #4 $230.49   7.502%   $247.7814   $247.78   $247.80   $247.80  
  Purchase #5 $83.76   11.712%   $93.57   $93.57   $93.55   $93.60  
  Purchase #6 $209.69   10.288%   $231.2629   $231.26   $231.25   $231.30  
  Purchase #7 $76.60   11.459%   $85.3776   $85.38   $85.40   $85.40  
  7 purchase totals = $919.15       $1,001.9734   $1,001.97   $1,002.00   $1,002.10