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 $166.58   10.623%   $184.2758   $184.28   $184.30   $184.30  
  Purchase #2 $178.93   8.767%   $194.6168   $194.62   $194.60   $194.60  
  Purchase #3 $85.48   11.823%   $95.5863   $95.59   $95.60   $95.60  
  Purchase #4 $194.41   6.702%   $207.4394   $207.44   $207.45   $207.40  
  Purchase #5 $60.73   7.740%   $65.4305   $65.43   $65.45   $65.40  
  Purchase #6 $118.99   6.407%   $126.6137   $126.61   $126.60   $126.60  
  Purchase #7 $41.90   9.767%   $45.9924   $45.99   $46.00   $46.00  
  7 purchase totals = $847.02       $919.9549   $919.96   $920.00   $919.90