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 $243.95   11.200%   $271.2724   $271.27   $271.25   $271.30  
  Purchase #2 $165.51   10.829%   $183.4331   $183.43   $183.45   $183.40  
  Purchase #3 $169.86   8.670%   $184.5869   $184.59   $184.60   $184.60  
  Purchase #4 $179.36   3.773%   $186.1273   $186.13   $186.15   $186.10  
  Purchase #5 $50.45   5.584%   $53.2671   $53.27   $53.25   $53.30  
  Purchase #6 $106.43   13.206%   $120.4851   $120.49   $120.50   $120.50  
  Purchase #7 $61.49   4.261%   $64.1101   $64.11   $64.10   $64.10  
  7 purchase totals = $977.05       $1,063.2820   $1,063.29   $1,063.30   $1,063.30