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 $53.86   11.431%   $60.0167   $60.02   $60.00   $60.00  
  Purchase #2 $11.83   6.151%   $12.5577   $12.56   $12.55   $12.60  
  Purchase #3 $211.68   12.847%   $238.8745   $238.87   $238.85   $238.90  
  Purchase #4 $224.46   5.606%   $237.0432   $237.04   $237.05   $237.00  
  Purchase #5 $36.95   3.258%   $38.1538   $38.15   $38.15   $38.20  
  Purchase #6 $21.72   7.173%   $23.278   $23.28   $23.30   $23.30  
  Purchase #7 $82.98   6.753%   $88.5836   $88.58   $88.60   $88.60  
  7 purchase totals = $643.48       $698.5075   $698.50   $698.50   $698.60