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 $88.75   12.250%   $99.6219   $99.62   $99.60   $99.60  
  Purchase #2 $234.52   13.352%   $265.8331   $265.83   $265.85   $265.80  
  Purchase #3 $112.38   13.630%   $127.6974   $127.70   $127.70   $127.70  
  Purchase #4 $167.84   5.500%   $177.0712   $177.07   $177.05   $177.10  
  Purchase #5 $20.69   4.604%   $21.6426   $21.64   $21.65   $21.60  
  Purchase #6 $219.49   3.202%   $226.5181   $226.52   $226.50   $226.50  
  Purchase #7 $49.96   12.129%   $56.0196   $56.02   $56.00   $56.00  
  7 purchase totals = $893.63       $974.4039   $974.40   $974.35   $974.30