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 $232.26   11.387%   $258.7074   $258.71   $258.70   $258.70  
  Purchase #2 $63.29   6.335%   $67.2994   $67.30   $67.30   $67.30  
  Purchase #3 $23.79   11.523%   $26.5313   $26.53   $26.55   $26.50  
  Purchase #4 $67.72   10.455%   $74.8001   $74.80   $74.80   $74.80  
  Purchase #5 $230.74   6.420%   $245.5535   $245.55   $245.55   $245.60  
  Purchase #6 $31.74   7.286%   $34.0526   $34.05   $34.05   $34.10  
  Purchase #7 $231.98   3.474%   $240.039   $240.04   $240.05   $240.00  
  7 purchase totals = $881.52       $946.9833   $946.98   $947.00   $947.00