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 $130.49   11.842%   $145.9426   $145.94   $145.95   $145.90  
  Purchase #2 $75.36   8.607%   $81.8462   $81.85   $81.85   $81.80  
  Purchase #3 $65.25   6.361%   $69.4006   $69.40   $69.40   $69.40  
  Purchase #4 $103.32   9.330%   $112.9598   $112.96   $112.95   $113.00  
  Purchase #5 $177.91   13.308%   $201.5863   $201.59   $201.60   $201.60  
  Purchase #6 $182.27   10.694%   $201.762   $201.76   $201.75   $201.80  
  Purchase #7 $143.72   4.427%   $150.0825   $150.08   $150.10   $150.10  
  7 purchase totals = $878.32       $963.5800   $963.58   $963.60   $963.60