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 $111.38   7.593%   $119.8371   $119.84   $119.85   $119.80  
  Purchase #2 $75.28   11.228%   $83.7324   $83.73   $83.75   $83.70  
  Purchase #3 $217.60   5.604%   $229.7943   $229.79   $229.80   $229.80  
  Purchase #4 $29.76   10.654%   $32.9306   $32.93   $32.95   $32.90  
  Purchase #5 $49.91   6.705%   $53.2565   $53.26   $53.25   $53.30  
  Purchase #6 $5.26   12.221%   $5.9028   $5.90   $5.90   $5.90  
  Purchase #7 $232.55   11.685%   $259.7235   $259.72   $259.70   $259.70  
  7 purchase totals = $721.74       $785.1772   $785.17   $785.20   $785.10