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 $103.36   12.263%   $116.035   $116.04   $116.05   $116.00  
  Purchase #2 $54.33   4.254%   $56.6412   $56.64   $56.65   $56.60  
  Purchase #3 $156.35   13.388%   $177.2821   $177.28   $177.30   $177.30  
  Purchase #4 $50.37   6.326%   $53.5564   $53.56   $53.55   $53.60  
  Purchase #5 $200.84   12.819%   $226.5857   $226.59   $226.60   $226.60  
  Purchase #6 $237.26   4.363%   $247.6117   $247.61   $247.60   $247.60  
  Purchase #7 $21.75   12.288%   $24.4226   $24.42   $24.40   $24.40  
  7 purchase totals = $824.26       $902.1347   $902.14   $902.15   $902.10