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 $247.46   6.143%   $262.6615   $262.66   $262.65   $262.70  
  Purchase #2 $120.48   12.675%   $135.7508   $135.75   $135.75   $135.80  
  Purchase #3 $32.25   13.552%   $36.6205   $36.62   $36.60   $36.60  
  Purchase #4 $240.91   13.699%   $273.9123   $273.91   $273.90   $273.90  
  Purchase #5 $92.81   4.216%   $96.7229   $96.72   $96.70   $96.70  
  Purchase #6 $105.27   5.423%   $110.9788   $110.98   $111.00   $111.00  
  Purchase #7 $158.79   4.782%   $166.3833   $166.38   $166.40   $166.40  
  7 purchase totals = $997.97       $1,083.0301   $1,083.02   $1,083.00   $1,083.10