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 $78.40   11.225%   $87.2004   $87.20   $87.20   $87.20  
  Purchase #2 $118.65   12.408%   $133.3721   $133.37   $133.35   $133.40  
  Purchase #3 $196.45   13.652%   $223.2694   $223.27   $223.25   $223.30  
  Purchase #4 $245.60   9.208%   $268.2148   $268.21   $268.20   $268.20  
  Purchase #5 $238.69   7.687%   $257.0381   $257.04   $257.05   $257.00  
  Purchase #6 $206.59   11.639%   $230.635   $230.64   $230.65   $230.60  
  Purchase #7 $22.88   10.200%   $25.2138   $25.21   $25.20   $25.20  
  7 purchase totals = $1,107.26       $1,224.9436   $1,224.94   $1,224.90   $1,224.90