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 $57.41   5.461%   $60.5452   $60.55   $60.55   $60.50  
  Purchase #2 $51.67   8.207%   $55.9106   $55.91   $55.90   $55.90  
  Purchase #3 $204.29   12.605%   $230.0408   $230.04   $230.05   $230.00  
  Purchase #4 $235.49   11.715%   $263.0777   $263.08   $263.10   $263.10  
  Purchase #5 $109.55   4.643%   $114.6364   $114.64   $114.65   $114.60  
  Purchase #6 $24.72   6.490%   $26.3243   $26.32   $26.30   $26.30  
  Purchase #7 $24.86   3.503%   $25.7308   $25.73   $25.75   $25.70  
  7 purchase totals = $707.99       $776.2658   $776.27   $776.30   $776.10