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 $92.25   5.151%   $97.0018   $97.00   $97.00   $97.00  
  Purchase #2 $23.32   3.702%   $24.1833   $24.18   $24.20   $24.20  
  Purchase #3 $123.41   12.309%   $138.6005   $138.60   $138.60   $138.60  
  Purchase #4 $56.26   8.380%   $60.9746   $60.97   $60.95   $61.00  
  Purchase #5 $159.56   6.581%   $170.0606   $170.06   $170.05   $170.10  
  Purchase #6 $11.64   13.785%   $13.2446   $13.24   $13.25   $13.20  
  Purchase #7 $56.72   9.698%   $62.2207   $62.22   $62.20   $62.20  
  7 purchase totals = $523.16       $566.2861   $566.27   $566.25   $566.30