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 $56.68   13.350%   $64.2468   $64.25   $64.25   $64.20  
  Purchase #2 $5.27   4.423%   $5.5031   $5.50   $5.50   $5.50  
  Purchase #3 $147.53   11.134%   $163.956   $163.96   $163.95   $164.00  
  Purchase #4 $223.42   5.611%   $235.9561   $235.96   $235.95   $236.00  
  Purchase #5 $203.75   8.629%   $221.3316   $221.33   $221.35   $221.30  
  Purchase #6 $247.32   11.529%   $275.8335   $275.83   $275.85   $275.80  
  Purchase #7 $85.41   3.224%   $88.1636   $88.16   $88.15   $88.20  
  7 purchase totals = $969.38       $1,054.9907   $1,054.99   $1,055.00   $1,055.00