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 $191.32   5.591%   $202.0167   $202.02   $202.00   $202.00  
  Purchase #2 $94.39   4.363%   $98.5082   $98.51   $98.50   $98.50  
  Purchase #3 $12.41   9.781%   $13.6238   $13.62   $13.60   $13.60  
  Purchase #4 $226.85   12.226%   $254.5847   $254.58   $254.60   $254.60  
  Purchase #5 $115.86   7.591%   $124.6549   $124.65   $124.65   $124.70  
  Purchase #6 $157.36   8.623%   $170.9292   $170.93   $170.95   $170.90  
  Purchase #7 $65.30   13.789%   $74.3042   $74.30   $74.30   $74.30  
  7 purchase totals = $863.49       $938.6217   $938.61   $938.60   $938.60