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 $172.83   11.788%   $193.2032   $193.20   $193.20   $193.20  
  Purchase #2 $43.88   3.795%   $45.5452   $45.55   $45.55   $45.50  
  Purchase #3 $137.70   12.637%   $155.1011   $155.10   $155.10   $155.10  
  Purchase #4 $119.88   4.824%   $125.663   $125.66   $125.65   $125.70  
  Purchase #5 $84.40   3.650%   $87.4806   $87.48   $87.50   $87.50  
  Purchase #6 $202.48   3.699%   $209.9697   $209.97   $209.95   $210.00  
  Purchase #7 $220.37   9.829%   $242.0302   $242.03   $242.05   $242.00  
  7 purchase totals = $981.54       $1,058.9930   $1,058.99   $1,059.00   $1,059.00